7.00pm: The 2012 GOP Iowa caucus is about to begin – it's all over bar the caucusing. And then the shouting. We will be bringing live results, analysis and speculation as they occur. How will the top three of Mitt Romney, Rick Santorum and Ron Paul finish? Does Rick Perry have a Texas Surprise under his big hat? Can Newt Gingrich's share of the vote match his sense of self satisfaction? And how many hours will elapse between the final result and Michele Bachmann's exit speech?

We will know the answers to all these questions and others in the coming hours. The caucuses themselves start at 8pm ET (1am GMT), and based on 2008 we should have the result by 11pm ET, or even earlier.

And don't forget that the Democratic party is also caucusing. It wn't be anything like 2008 of course but it's worth remembering that the Republicans are not the only show in town.

The Guardian has correspondents in Iowa and New Hampshire, watching the results and talking to voters. And we have a raft of comment from the inestimable Ana Marie Cox.

And we want comments from you, the reader, right here. We'll be reading them all and passing the best jokes off as our own.

Read our earlier live coverage from today's campaigning in Iowa.

7.10pm: What are the five things to look for in tonights Iowa GOP caucus results?

1. The winners: Obviously, who finishes first is important. For an insurgent challenger such as Rick Santorum it's vital – no one remembers the second place finisher. Who finished second in 2008? Mitt Romney. Now, it's true that winning in 2008 didn't exactly make Mike Huckabee the nominee but without that "winner" title Huckabee would have faded into obscurity.

2. The losers: As they say, it's not the taking part that counts, it's the losing. Sixth place finish is almost certainly a ticket home – and that's most likely to be Michele Bachmann. But what about the fourth and fifth places? There's losing and there's losing: third place by a whisker and third by a mile can make the difference between going to New Hampshire or becoming a Fox News studio guest.

3. Turn-out: How many Iowans made it to the caucuses after all the hoopla? For the Republicans the benchmark is the 118,400 in 2008 – a figure that paled alongside the Democrats total of 227,000. That has implications for the general election.

4. Republican base: The make-up of the Republican voters will tell an interesting story, particularly for the fortunes of Mitt Romney and Rick Santorum, both of whom need to expand their support outside their natural base of traditional Republicans (for Romney) and social conservatives (for Santorum).

5. Democrats: The Democratic party is also caucusing tonight, although there is no such drama, Barack Obama being unopposed other than by sundry unknowns. But the party is using the night as an exercise in motivating and turning out its base in Iowa.

7.44pm: We just heard Michele Bachmann make her final pitch at an actual caucus site in Iowa, in which she railed against "socialised medicine". And to think she wants to be the Margaret Thatcher of America, given the Iron Lady's record on the National Health Service.

Now up: Newt Gingrich, who sounds like he's furious.

7.52pm: Our reporter Adam Gabbatt is at a caucus location at Valley High School in West Des Moines, Iowa, and has been speaking to early arrivals.

Amy and Mike Hoffmann were among those arriving early for the Republican caucus at Valley High School, in West Des Moines. Both will be voting for Newt Gingrich tonight, despite the millions his rivals have spent on television adverts targeting the former House speaker.

"It's just his experience," Amy said, adding that she had made her mind up a month ago.

The couple, who are both attorneys for workers' conpensation, were Cain supporters, "but obviously he's not in the race any more".

Amy said the negative advertising had not shaken her faith in Gingrich: "I think he has some good explanations for the ethics violation." Her husband added: "He has more experience in the position of power from being speaker."

That's it – Rick Santorum's campaign is obviously in trouble. He's dropped the sweater-vest at the 11th hour, reports Scott Conroy of RealClearPolitics.

Fans of Santorum with a schoolboy sense of humour will be delighted to hear that Santorum is in Johnston at the caucus there.

8.00pm: I have been e-chatting with Ana Marie Cox:

Me: Can you sum it up in a word?
Ana: The caucuses?
Me: Yes
Ana: I've been using "finicky" a lot. "Petulant"?

So there we have it: the words of tonight are "finicky" and "petulant". Which sums it up nicely.

8.01pm: A CNN reporter is shoving a mic under Newt Gingrich's nose and asking dumb questions like: "Do you think you will win Black Hawk county?" To which Gingrich rightly shrugged and said "Yeah."

8.04pm: Voting is under way! And we have a live-updating results page. Which is much more elegant than Google's.

8.06pm: No exit polls tonight, but CNN has an "entrance poll" – a survey of caucus-goers entering their caucusing sites. And OH MY GOD the top three are Mitt Romney, Rick Santorum and Ron Paul.

"You can think of this as the most recent poll in Iowa, really," says Wolf Blitzer, but you tell his heart isn't really in it.

8.10pm: Steve Grubbs, former chairman of the Iowa Republican party, and unlucky enough to have been chairman of the Herman Cain campaign in Iowa, tweets a picture of his ballot paper.

8.18pm: Adam Gabbatt has taken this paorama picture of the scene at Valley High School in West Des Moines, as caucus-goers get ready for proceedings to get under way.

A Rick Perry supporter leaves a caucus training session at the Sheraton hotel in west Des Moines. Photograph: Jonathan Gibby/Getty Images

8.19pm: MSNBC has what it is calling an exit poll but must also be an entrance poll, given the timing. And based on this, the Ron Paul supporters showed up early and so make it look like he's done very well. Which he might have.

8.25pm: CNN is showing its "early voters" entrance poll, which reveals:

Ron Paul 24%
Mitt Romney 24%
Rick Santorum 18%
Newt Gingrich 13%
Rick Perry 11%

Warning: you know who was leading in the early entrance polls in 2008? Hillary Clinton, that's who. And she finished third in the end. And let's not forget early vote winner John Kerry in 2004 in Ohio.

So if you've got a dose of salt, take it now. And then the tequila.

8.29pm: On that note, Professor Larry Sabato points out another Iowa entrance poll "winner" from 2008:

Add more salt.

8.30pm: For those of you who really want to get down in the weeds for the caucus results that will shortly come gushing forth, then read this piece from the Washington Post, naming the six counties to watch.

After reading this you can stroke your goatee and state gravely: "Of course it all comes down to Polk County, which – if my memory serves me correctly [smile wanly] – accounts for upwards of 20% of the statewide caucus vote. Pass the PBR."

Republican presidential candidate Mitt Romney greets supporters at a final rally Monday night before the Iowa caucuses on Tuesday. Photograph: Bob Daemmrich/Bob Daemmrich Photography, Inc./Corbis

8.37pm: I'm hearing rumours that the Gingrich campaign has failed to get speakers or literature to a number of big caucus sites. CNN also says Perry failed to get speakers at a couple of places. Interesting.

8.39pm: The Associated Press bothers to watch Jon Huntsman, exiled to New Hampshire:

Even before the results were in, Republican presidential hopeful Jon Huntsman had a message for whoever won the Iowa caucus: "Welcome to New Hampshire. Nobody cares."

Republican presidential candidate Jon Huntsman, accompanied by his wife Mary Kaye, tours the Tidland Corporation in Keene, New Hampshire. Photograph: Matt Rourke/AP

8.42pm: Actual votes! From Warren County. With 4% of the caucuses counted, Ron Paul has 50% of the vote. That's nine actual votes.

So I'm ready to declare Ron Paul is the … oh no let's wait for a bit.

A voter registers at a caucues at a school in Des Moines, Iowa. Photograph: Jewel Samad/AFP/Getty Images

8.43pm: The New York Times is running the numbers from the entrance/exit/shake it all about polls:

Another key finding in the entrance polls so far: almost 30 percent of voters identify as either independent or Democratic, much higher than in 2008 and toward the high range of the estimates that pollsters made in their likely voter models. The entrance polls report that about half of those voters are breaking for Ron Paul.

Likewise, the percentage of moderates according to the the exit polls is about 20 percent - twice as high as in 2008 - and those voters so far are breaking for Mr. Paul as well.

8.50pm: Reporting from Valley High School in West Des Moines, Adam Gabbat has been talking to more voters.

Peter Potycki is "still undecided", having narrowed his options to
Michele Bachmann and Rick Perry. "Both are good," Potycki said, citing the fact Bachmann has "worked really hard" and Perry's stance on "kicking out all the illegals".

8.57pm: In case you ever wanted to know what a British general election was like, it's pretty much like Iowa at this point: television shots of people counting bits of paper.

Voters register to cast their ballots during republican caucues at a school in Des Moines, Iowa. Photograph: Jewel Samad/AFP/Getty Images

9.01pm: According to the Iowa GOP running tally of precincts reporting, it's Paul on 25%, Romney 23%, Santorum 23%, Gingrich 13%, Perry 9%, Bachmann 6%. Which is all pretty much as the polls suggested.

But beware, that's only about 5% of the votes so far.

9.04pm: Buzzfeed has caught the Ron Paul campaign levelling some ungentlemanly criticism at Jon Huntsman, who is ignoring Iowa and campaigning in New Hampshire. The tweet, now deleted, reads: "@jonhuntsman we found your one Vota in Iowa, he's in Linn precinct 5 you might want to call him and say thanks."

Thanks to Twitter's new functionality, if a website embeds a tweet, the content remains on that website even if the original tweet is deleted. Remember folks, tweets never die!

9.14pm: With 14% of the precincts in Polk County reporting, Ron Paul has 29% and Romney 25%. Now stroke your goatee and nod sagely.

9.17pm: Well then, with 16% of the caucuses in, precisely 1.2 percentage points are between Ron Paul, Mitt Romney and Rick Santorum. In other words: ?

9.21pm: Adam Gabbatt has been filming the vote-counting on stage at precinct 3, at Valley High School in West Des Moines.

Overheard: "Here's a Bachmann."

9.34pm: Guardian sage Ana Marie Cox has her thoughts on what we have learned tonight.

The most entertaining thing about the caucuses so far is the lengths to which the news networks will go to make them interesting. CNN has hushed-voice narration of people counting ballots ("they're counting the ballots") and a numbing assortment of banners across the bottom of the screen. MSNBC has gone with an orchesteral approach, asking a chorus of pundits to share the same set of opinions with us over and over. And Fox is busy convincing everyone that Iowa doesn't really matter (unless Romney wins).

The exit and entrance polls produce surprisingly little drama, because that would mean commentators admitting they didn't see the results coming. Paul's strong showing keeps getting brushed aside as an expected outcome, which of course must be true: Remember all the interviews and magazine covers he got last summer, and how seriously he was taken at the debates?

A Paul win, as I've written before, would actually be a rejection of the entire narrative that the media has forced upon the GOP primary. Paul voters, according to those CNN polls, are young people, are independent, but are also evangelical and conservative. All of those groups feel strongly that what they see and hear on the news is biased against them, and are a set of voters for whom "electability" is a side issue. They want to express themselves, and it seems as though they have.

9.36pm: There's some fascinating intra-mural debating going on via Twitter between Republicans, over what the results might be. Basically, the more traditional Republicans (such as Ari Fleischer, Karl Rove), seem to be saying that even a Romney third place is fine, while Romney boosters are reminding us that St Ronald Reagan lost Iowa and, so big deal. Meanwhile, the younger Republicans (such as Erick Erickson) are saying that would be bad news for Romney.

9.37pm: RESULT: In Boone County, Rick Santorum wins with 30%, followed by Ron Paul with 20% while Mitt Romney limps in with 17%.

Rick Perry edges out Gingrich for fourth place by 0.7%.

9.44pm: In 2008, Romney got 21% from Boone County. So he's underperformed compared with 2008. And that is going to be a crucial stat for him: if Romney does significantly worse than in 2008, that will be seen as a loss for him, no matter what else happens.

On the other hand, Santorum has underperformed Mike Huckabee in Boone as well, but then that end of the spectrum is more crowded in 2012 than in 2008.

9.44pm: On Twitter, Larry Sabbato throws his hands up.

9.50pm: Rick Perry's supporters in West Des Moines are unfazed by his poor perforamnce in early results. Speaking to Adam Gabbatt are Kelsey Orr and Ginger Howard.

9.51pm: Sam Stein of the Huffington Post makes a tasteful joke about this being the first three-way that Rick Santorum has ever been in.

An all-male three-way at that, Sam.

9.55pm: With 31% of precincts reporting, just 189 votes separate Ron Paul in third place and Mitt Romney in first place.

9.56pm: Oh dear: Jon Huntsman has only 211 votes so far. "Other" has 228. And we all know who "other" is, right? Yes! Stand by for the Sarah Palin surge!

10.04pm: "Tonight we've been focusing on the Republicans," says Megyn Kelly on Fox News, "however there is something going on over on the Democratic side," with a barely concealed note of disappointment.

Oh dear, here's Evan Bayh the former Democrublican senator. He tells us that the losers are those finishing fourth, fifth and sixth. God, what a loss he is to the nation.

Supporters of Republican presidential candidate Mitt Romney watch election returns at a hotel in Des Moines, Iowa. Photograph: Tannen Maury/EPA

10.04pm: Former Bush administration spinmeister Ari Fleischer says of Michele Bachmann's dismal showing in Iowa: "To paraphrase Frank Sinatra, if she can't win it there she can't win it anywhere."

10.12pm: More from Adam Gabbatt at the Valley High School caucus in West Des Moines, who spoke to voters Anna and Peter Marasco at precinct 3, where the former Massachusetts governor Mitt Romney won convincingly.

Anna, 66, said: "Peter and I both voted Romney. He's an excellent candidate. He has great experience, a good family man. He's been a businessman, been running his own business."

Peter, 78, who was born in Italy – his wife was born in Germany –  added: "I believe he's a good man. I thought he would definitely win."

Romney took 141 votes at the caucus here, with Gingrich the runner-up with 52 and Ron Paul on 51 – it looks as if this is not being reflected in the total
count however.

10.27pm: The Guardian's Ewen MacAskill is watching the scene at Des Moines:

I'm at the main media centre in Des Moines, surrounded by hundreds of journalists, none of whom has a clue who is going to win. Network TV journalists have to go on camera to say something, even though they it is so tight they are struggling to find a coherent line. I am as ignorant as the rest of them, but enjoying the dead heat. The Des Moines Register poll on Saturday, at this juncture, was not far off the mark.

10.28pm: In Emmet County in the far north of Iowa, "Other" has won the county with 35%. That's 175 votes in total, so it's no a big place. Palin surge!

Seriously, "No Preference" got more than 12%. Rick Santorum came second with 13%.

10.29pm: With nearly 50% of the votes in, Fox News is making the confident projection that Newt Gingrich will finish fourth, and Rick Perry will finish fifth. They have already pinned Michele Bachmann down to sixth place.

What sort of race is it where the losers finish first?

A voter reads a Ron Paul campaign booklet as he waits to casts his ballot during republican caucues at a school in Des Moines, Iowa. Photograph: Jewel Samad/AFP/Getty Images

10.35pm: Romney is running away with Dallas County, the major suburban area of Des Moines, with over of 90% of precincts reporting. Romney has 32%, ahead of Santorum with 20%. But that's bang on his 2008 performance. He's not moving the ball down the field, as they say in the NFL.

10.36pm: By this point in 2008 we knew that Mike Huckabee had won on the Republican side and we were waiting for the full count to see if some kid named Barack Obama was going to win on the Democratic end. Happy days.

Man, I was doing this exactly four years ago? And on my birthday too.

10.42pm: The latest summary from AP with 878 of 1,774 precincts declared – that's 49%

Rick Santorum 13,594 – 24%
Mitt Romney 13,204 – 24%
Ron Paul 12,205 – 22%
Newt Gingrich 7,426 – 13%
Rick Perry 5,671 – 10%
Michele Bachmann 3,140 – 6%
Jon Huntsman 313 – 1%
Other 229 – 0%

10.53pm: Pow! After hiding quietly in the background, Sioux County reported all in a rush – and a huge win for Santorum in the most conservative, most Republican part of the state.

Mike Huckabee won it in 2008 with 53% – and Santorum did pretty well to get 45.5% this time. Romney only got 14% - exactly the same as in 2008.

So Romney appears to have made zero progress in winning over the guts of the Republican party, despite all that effort and sucking up. Indeed Romney nearly got eclipsed by Rick Perry of all people, holding him off by 0.1 percentage point.

OK, this isn't going so well for Romney.

10.54pm: Ewen MacAskill reports from Des Moines, looking at what it means for the GOP nationally:

Unless there is a sudden surge at the end for one of the candidates, it is shaping up as disastrous night for the Republican field. It confirms voters are pretty unenthused by the field, with no clear candidate to take on Obama. The tight finish makes a protracted race more likely, to the delight of Democrats, who will happily watch the Republicans eat up funds and energy fighting with one another for month after month.

There is a theory that long campaigns make candidates tougher: think Obama versus Clinton. But most Democrats would have been happy with either. The problem for the Republicans is the high dislike of so many in the field.

Mitt Romney is still the likeliest to emerge as the nominee but it is pretty grim if the best he can do is about 25% of the Iowa caucus-goers: that is not anendorsement. If he cannot enthuse Republicans, is he going to fare any better with independents? He has to hope independents will prove to be an easier sell than the Iowan Republicans, dominated by Christian evangelicals and Tea Party members.

Santorum is going nowhere after Iowa, with no organisation or funds behind. Paul has a strong following that will deliver about 10% for him among Republicans nationwide but is incapable of winning the nomination or the general election, with the highest negatives of any of the Republicans in the field.

Gingrich and Perry, especially Perry, total flops but will keep on going through South Carolina and Florida. Worst night of all for Bachmann, not least because she is only one born in Iowa.

end quote

10.54pm: God damn it's close out there. With 87% of the precincts counted, it's Santorum 24.6 and Romney 24.5. Ron Paul back at 21%.

10.56pm: Our Chicago-based columnist Gary Younge has these thoughts on the night.

So long as it stays this close then the night's winner will be Rick Santorum and the long term loser will be Mitt Romney. Even if Santorum comes third he is the little tea party tortoise that could. He didn't peak so early that he would wilt under media scrutiny (that has yet to come) but crested in time for the actual vote rather than the polls.

Assuming Bachmann bows out now and Gingrich – who is broke – limps to South Carolina then the right will coalesce around him. It's unlikely he'll win the nomination, but given the greater proportionality, he'll stay in the game which means the tea party retains some electoral relevancy.

Conversely even if Romney wins in Iowa it won't be by enough to persuade anyone that he is actually the Republican choice as opposed to its default. True, he stayed away until the very end, but this is a weak field in a state Republicans would want to win back come November. Polls suggest his inability to break 25% is not a local problem. Most Republicans just don't like him.

A Paul win would certainly muddy the waters, but it hardly changes the general flow.

We'll have a full column by Gary on the Guardian website tomorrow.

11.07pm: I hear that behind closed doors, Mitt Romney is onto his second caffeine-free diet coke of the night.

11.08pm: Fox News, NBC and ABC are now projecting that Ron Paul will finish in third place.

And then there were two....

11.09pm: It has come down to this: Mitt Romney or Rick Santorum. It's like that spoof soccer World Cup final ad in the Simpsons: "The game that will decide once and for all which is the greatest nation on earth: Mexico or Portugal."

Rick Santorum supporters at his restuls party in Johnston, Iowa. Photograph: Andrew Burton/Getty Images

11.14pm: Adam Gabbatt has moved on to Rick Santorum's party in Johnston, ten miles north-west of Des Moines.

There's a growing crowd of revellers and an even faster growing crowd of journalists. Among the former is Sandy Hoffman, a supply teacher at Valley high school, where Santorum made an appearance this morning.

Hoffman was undecided until she net Santorum for herself: "I got to talk to him, it was just his sincerity, I was so impressed." "He gave me a firm handshake and looked me straight in the eye. I was like: 'I like this guy.'"

11.17pm: Well, Ron Paul didn't do the Dean Scream but he did bang on about the gold standard. Some are predicting that on Paul will rake in a fundraising bounce after tonight.

11.22pm: With 92% of the count in, Mitt Romney leads Rick Santorum by 13 votes. Yikes.

11.29pm: If Mitt Romney does win this, the psychology of winning such a tight race is an inevitable boost. In 2008 he lost all the close ones. If he does take first place here it will be because he outperformed his 2008 campaign in Polk County substantially, in the part of Iowa that most resembles most of America's contested states in a presidential election.

11.34pm: Newt Gingrich has just given one of his more impressive speeches, pausing only to rip Mitt Romney for his campaigning. Gingrich is running full-page ads in New Hampshire newspapers tomorrow, going full-bore at Mitt Romney.

11.39pm: Back to Adam Gabbatt at the Santorum party in Johnston, Iowa. He's been speaking to Santorum supporter Jim "Bob" Duggar, who is at the results party with a large proportion of his "19 and counting" children.

Duggar, left, "really did believe" Santorum would do this well in Iowa. "Because people would see he is he family values candidate we all need to get behind."

Packed into an increasingly warm function room at the back of the Stony Creek Inn in Johnston, Duggar said Santorum was reaping the benefits from meeting people "one on one, showing people he's a genuine person".

Duggar, whose reality television show follows the inevitable travails that come with raising 19 children, said he expected Santorum to consolidate the religious vote as Bachmann and Perry drop out.

Of the tight vote: "It is just nip and tuck. But even if Rick was five points down, that would still be a loss for Romney. He's spent millions on this."

Republican presidential candidate Rick Santorum looks over Iowa caucus returns in his hotel room. Photograph: Charlie Riedel/AP

11.46pm: Bad news for Mitt Romney from Woodbury County. In 2008 that was his stronghold, winning 38% of the vote in a big county. Tonight he got shellacked by Santorum, who got 32% while Romney had just 28% with 95% of the votes in.

11.50pm: "There you have it, a clearly tired Michele Bachmann," says Fox News's Megyn Kelly having watched Bachmann's speech just now, in which Bachmann thanked God for bringing America into existence.

But no signs that Bachmann is dropping out yet. Although AP is reporting that her campaign manager says she might. Who knows! It's Michele Bachmann, she doesn't play by anyone else's rules.

11.57pm: So: 96% of the votes are in and its Rick Santorum on 24.7% and Mitt Romney on 24.6%.

11.59pm: Adam Gabbatt has been speaking to Jan Boender, who entertained the whole Santorum family at her farm in Oskaloosa, south east of Des Moines, in July.

"He needed a place for his family to stay while he was campaigning," Boender said as the crowd here, following the results on television, occasionally whooped in a Santorum success.

While Santorum Sr campaigned his seven children "fished and worked on the farm".

Boender wasn't decided on a candidate before Santorum's stay, but found him "very personable", and has since got behind him, citing his "knowledge and experience".

Santorum stayed in Boender's 'Stillwaters cabin' for a week, with a particularly fond memory for Boender being the night the apparent star of the Iowa caucus cooked dinner for her family of 26 - grandchildren included.

"He and his family cooked barbecue beans, pork, chicken, he picked some sweetcorn off the farm and boiled that," Boender said.

Asked of she imagined then that Santorum would be leading the vote tonight, she said, simply: "No".

"This is a miracle. But he has all the abilities to be president."

12.09am: And in case you were wondering, if the result is this close then the whole caucuses will have to be done over … no, thank god. Just as there is no basement in the Alamo, there are no recounts in the Iowa caucuses. That's official.

Rick Perry yard signs stacked against a wall at his Iowa Caucus rally in West Des Moines, Iowa. Photograph: Samantha Sais/REUTERS

12.10am: Rick Perry has been speaking, and began by reading a letter from a supporter about what a great guy he is.

He's fifth placed here, now he says he is going back to Texas to pray and reflect. That sounds like he's minded to drop out – but we'll see.

12.10am: What are we waiting on? According to AP, there's a guy in truck driving some results from Story County, where only 55% of the precincts have reported. So: Rick Santorum leads Mitt Romney by 40 votes overall and we are all waiting on a guy in a truck. Great.

Don't stop for coffee, guy in truck.

12.13am: Our correspondent Ewen MacAskill was watching Rick Perry and thinks Perry is off back to the ranch:

It sounded to me as if Rick Perry is about to quit. No-one serious about fighting on would say they were having a rethink. One of the strangest stories of this campaign is what a flop he has been. On paper, he had all the credentials, but he did not measure up. I saw him on Monday night in Iowa, Perry, and he gave a poor speech, the rhetoric over the top and the delivery hammy.

12.15am: On Fox News, Joe Trippi – Howard Dean's 2004 guru, so you know, a great source of advice – reckons that Santorum should just go on TV right now and given a speech and claim that he was the winner, even if the votes haven't all been counted and he risked eventually losing.

Karl Rove agrees. So there you are, two political geniusies (well one, Rove), basically saying that Santorum should just go public with a whopper. Tells you a lot. Maybe Santorum should hang up a "Mission accomplished" sign? That works, right?

12.16am: And obviously the Santorum campaign are taking their advice from Fox News because they have just announced that Rick will appear in a few minutes.

12.18am: Whoop whoop!: Buzzfeed Politics has a scoop:

Arizona Senator John McCain, his party's 2008 nominee, will endorse Mitt Romney in New Hampshire tomorrow, a well-placed former McCain aide told BuzzFeed Tuesday.

McCain and Romney were bitter foes in 2008, but Romney repaired the relationship after his defeat with a season of determined campaigning for his former rival.

The endorsement will offer the Romney campaign a pivot point after the virtual tie with Senator Rick Santorum in Iowa, and a growing impression that the former governor is uniting the party behind him.

Well now, that is a double-edged sword. As Buzzfeed notes: "McCain is unlikely, however, to appeal to the conservative Republicans who are skeptical of both men."

12.24am: Here's Rick Santorum coming on stage at his victory party.

"Game on," is his first words. Big cheers. But then he quotes CS Lewis in praising his wife. It's quite sweet. Then he thanks God and then Iowa. "You, by standing up and not compromising, by being bold and leading … you have taken the first step in taking back this country," he says to Iowa.

"I never forget the first time I saw someone that had died," says Santorum. Downer man.

12.28am: With 98.3% of the vote in, Mitt Romney has retaken the lead from Santorum: by 41 votes. My guess is he'll win from here on in. The few remaining counties are mainly Romney supporting at this point, so he'll likely keep gaining votes, barring a miracle.

So yeah, I'm calling Iowa for Mitt Romney. Sue me, Associated Press.

Rick Santorum speaks during a rally with supporters on Iowa caucus night at the Stoney Creek Inn in Johnston, Iowa. Photograph: Scott Olson/Getty Images

12.33am: Scratch that: suddenly 98.6% of the votes are in and Rick Santorum is up by FIVE VOTES.

Santorum: 29,662
Romney: 29,657

12.44am: Over to Adam Gabbatt in Johnston, Iowa, who watched Rick Santorum speaking.

The crowd here at Stony Creek Inn gave a huge welcome for Santorum as he entered, flanked by his family.

Santorum quoted the spiritual author CS Lewis, thanked his wife - "his best friend" - God, and the voters of Iowa. His speech went down well... but as
he was talking, a television in the corner of the room has ticked over and is now showing Romney in the lead.

People are listening intently, most apparently unaware. Santorum hasn't declared himself the winner – but many here currently think he is.

12.45am: Despite my earlier wobble, I still think Mitt Romney will squeak it. The outstanding counties where he is leading are bigger than the tiny ones that Santorum is leading in, especially Johnson County, a big county where Romney is whipping Santorum by two to one and about 5% has still to come in.

12.47am: Now Romney is speaking, which he had to do as soon as Santorum left his stage. Romney is in full suck-up mode. "This is a campaign night where America wins," says Mitt. Loser.

Romney is just giving his usual campaign speech about how awful Obama is. Jolly good.

Apparently, according to the journalists watching, the Romney campaign set up a teleprompter before the candidate appeared, and then hurriedly took it down. Hmm. So that's why Mitt's gone with the stump speech, rather than say anything much about Iowa or whatever.

12.59am: How close is it? This close:

Not that it matters other than for bragging rights, since the proportional allocation rules means they get the same delegates eventually.

1.08am: My colleague Ewen MacAskill informs us that tonight's turnout was a record for Iowa Republicans of 120,000 caucusees, but not much over 2008's 118,000. Still miles behind the Democratic party turnout of 2008.

1.09am: Google and CNN now say: Santorum 29,935, Romney 29,916, with five precincts left to report. Just 19 votes are between them.

This calls for more tea. It's 6am in the UK: hello Britain.

1.14am: Dear lord: there are just two precincts left to count. Rick Santorum is up by 18 votes. One precinct is in Keokuk County where Santorum is ahead, the other one in Clinton County, which has Romney up so far. More votes in Clinton.

1.20am: So we are all waiting for one precinct in Clinton County to report, which will decide a race between two candidates separated by 18 votes.

Typical American politics, it all turns out to be about Clinton.

In Clinton County, with 96.7% of the precincts counted already, Romney has 386 votes and Santorum has 321. One precinct remains uncounted.

Daily Kos Elections says Romney has been averaging a net gain of 10 votes per precinct in Clinton city. So it's not insane that he picks up 18 votes although unlikely.

The other precinct is tiny, although since every vote counts, who knows? Indeed, Daily Kos Elections (who are fantastic at this stuff, as you may have noticed) says the last Keokuk County precinct in Sigourney city. Sigourney city is actually 37-20 Romney currently.

Oh boy. Mitt Romney picked the wrong week to give up lemonade.

1.31am: Rick Perry's spokesman says the Texas governor won't make a decision about whether to continue until Thursday.

1.33am: Spooky:

Now, what are the odds of that?

1.34am: Jeff Zeleny of the New York Times appears to give the Iowa result to Romney in the long term:

The Iowa caucuses, which sounded the opening bell of the Republican contest, did not bring the clarity to the nominating fight as Mr Romney had hoped.

But even though he did not secure the authoritative victory that he had fought for in the last week, he handily dispatched two rivals who were once seen as his biggest threats, Mr Perry and former House Speaker Newt Gingrich.

Tthis is strange: the Iowa GOP have just updated the vote totals, but still have two precincts remaining uncounted.

The new vote total has Mitt Romney in the lead by ONE VOTE.

But what is this? It's the missing Keokuk County precinct! And it gives a massive five votes for Santorum!

So, with one precinct out, Santorum leads by FOUR VOTES.

1.54am: So there's one precinct left in Clinton city, which @fivethirtyeight makes a smart guess to have 75 votes uncounted. Mitt Romney needs to gain a net five votes more than Santorum.

Fox News is terrifying people with tales of a lost precinct in Clinton County, and now Karl Rove is saying that there may have been under-counting in Story County.

There was a case in 2008 where a caucus precinct captain went home and forgot to report their total, I vaguely recall.

1.59am: Can I be the first to accuse the Republican party of massive electoral fraud to deny Ron Paul the nomination?

Somewhere in a basement in Clinton city, Karl Rove's minions are stuffing a ballot box with enough votes for Mitt Romney to win.

Start your conspiracy theory engines now!

2.06am: The tally from Story County has been corrected officially, cutting Santorum's lead to four.

And, according to Karl Rove on Fox News, the votes from the final precinct in Clinton County have been "agreed" between the Santorum and Romney camps, giving Romney a win by 18 votes.

So, that means:

Romney wins Iowa by 14 votes!

2.18am: So the cause of all this delay was the Clinton County Republican party. A random search via Google brought me to its website – and they really sound like a fun bunch.

Correction: as various readers have pointed out, that website above is for another Clinton County Republican party, specifically Clinton County, Michigan. Sorry, good people of the Clinton County Iowa GOP, whose website is here.

2.34am: The GOP has confirmed that Mitt Romney has won the Iowa caucus with 30,015 votes, with Rick Santorum eight votes behind on 30,007.

2.45am: And that's it. Here's a final summary:

• Mitt Romney has won Iowa caucuses by a sliver over Rick Santorum, after a long and often farcical night of voting. The former Massachusetts governor took 30,015 votes, and Santorum was only eight behind on 30,007. Santorum capitalised on a late surge in the final days before voting, competing neck and neck with Romney who ended up with a lower share of the vote than in 2008.

• Rick Perry retreats to Texas to reconsider his continuation in the GOP presidential race, with suggestions that he will withdraw on Thursday. Newt Gingrich vows to "tell the truth" in aggressive campaign aiamed at Romney in New Hampshire.

• Iowa Republicans post a record caucus turn-out of 122,000 – but only 3,000 more than in 2008.

So, Romney won the Iowa caucuses by a squeaker: eight votes out of a total of 122,000. But a win is a win: Romney gets to call himself a winner, as opposed to the "silver medal" he awarded himself in Iowa in 2008.

But that's about it. The result was so close that he can't take any comfort yet he gets the label of front-runner hung upon him. And being the front-runner is not a comfortable place to be in this Republican primary season.

Next is New Hampshire, and there Romney has a big lead in the polls. That can only shrink when it gets nasty, as Jon Huntsman, Santorum and an angry Newt Gingrich come after him.

And the Iowa effort came at great cost, financially. The Romney campaign spent at least $4m for less than 25% of the vote. That's $4m he can't spend anywhere else, not to mention the millions more his Super Pac supporters burned through in attacking Gingrich.

Santorum surely got the biggest boost of this endless night of Iowa voting. He has come from nowhere and came within a whisker of winning.

Buzzfeed has an excellent illustration of the cost of victory: Romney's campaign spent $156 per vote, while Santorum spent just $21 and got a lot more value for money. Now a lot more Republicans will be taking a second look at him.

We have no way of knowing how this campaign will pan out. But next up are New Hampshire and South Carolina, and all that has happened is that Romney's rivals – other than Rick Perry, who will surely drop out – have been emboldened rather than flattened.