House Speaker John Boehner just wanted to sneak out of the White House for a smoke.

But President Barack Obama pulled him aside for a grilling. Obama wanted to know why they were in the second day of a government shutdown that the speaker had repeatedly and publicly pledged to avoid.

“John, what happened?” Obama asked, according to people briefed on the Oct. 2 conversation.

“I got overrun, that’s what happened,” Boehner said.

(WATCH: Who won the shutdown? Top 5 quotes)

It may be the most concise explanation of a chaotic, 16-day standoff that prompted the first government shutdown in nearly two decades and ended only hours before the world’s largest economy nearly exhausted its ability to pay the bills. The fiscal drama turned on a series of complicated relationships, internecine Republican warfare and rare Democratic unity.

The House Republican conference ran roughshod over Boehner, a 22-year veteran of Washington who started the fight demanding to strip funds for Obamacare but settled in the end for the reaffirmation of a minor provision already in the law.

(PHOTOS: The government reopens)

He was overtaken by Senate Minority Leader Mitch McConnell (R-Ky.), who swept in near the end to forge a bipartisan agreement, part of an attempt to shield Republicans from further damage and salvage his party’s chances of winning back the Senate next year.

A particular low point came Oct. 1 when Democrats released private emails to POLITICO aimed at making Boehner look like a hypocrite. The emails showed that Boehner had actually been deeply engaged in fixing an Obamacare glitch that would have cost lawmakers and their staff thousands of extra dollars. Hill veterans weren’t quite as shocked by the flip-flop as the utter breakdown of decorum between Senate Majority Leader Harry Reid (D-Nev.) and Boehner.

(Also on POLITICO: Obama’s latest push features a familiar strategy)

Above all, Republicans never believed Obama would hold firm on his refusal to negotiate and Democrats would maintain an unusual level of cohesion — united by a visceral desire to put the tea party in its place and an almost mama grizzly instinct to protect Obamacare.

“It was not a smart play,” McConnell said Thursday of the GOP’s Obamacare strategy. “It had no chance of success.”

Obama and Reid stuck together, emerging as the political victors. Their hard-ball tactics were designed to “break the fever” brought on by the tea party, but it also helped drive the country to the edge of default.

Republicans cycled through every option possible during the three-week standoff to save face. Their Obamacare demands devolved from repeal and defund to a delay of the individual mandate. They revived the idea of a “grand bargain” on taxes and government spending but Reid openly laughed when Boehner raised it during a White House meeting. They offered a more narrow proposal to replace the sequester cuts for two years. Then, they went back to Obamacare.

(PHOTOS: Mitch McConnell and Harry Reid’s friendship)

Nothing worked.

When things were at their worst, some Republican senators urged Vice President Joe Biden to get more involved. But he told each of them it wasn’t his call. Biden participated in meetings at the White House but Reid, still angry about the vice president’s concessions during the fiscal cliff talks last December, had shut him out of direct negotiations with lawmakers this time around.

By Wednesday, Republicans just needed a way out, agreeing to a bill that looked almost identical to what they rejected three weeks earlier: a debt-limit increase until Feb. 7, an extension of federal funding through Jan. 15 and no binding strings attached.

(Also on POLTICO: Shutdown aftermath: John Harris, Todd Purdum assess damage)

This account of the behind-the-scenes drama was drawn from dozens of interviews with key players in Congress and at the White House. The look back reveals how Republicans waged a fight on Obamacare that their leaders knew they would probably lose but pushed anyways because many in their ranks truly believed that Democrats, like they’ve done so often before, would fold — especially under the threat of an historic default on U.S. debt.

McConnell told his colleagues this week that his party should “never” be put in the same political position again.

“We fought the good fight,” Boehner told WLW radio on Wednesday. “We just didn’t win.”

(PHOTOS: John Boehner’s life and career)

The buildup to shutdown

Any hope of an easy debt limit extension was dashed in late August when Boehner promised a “whale of a fight.”

Obama and Reid got on the same page early on, agreeing during strategy sessions over the summer that they wouldn’t give up anything until Republicans renewed the debt limit and government funding.

Democrats never believed that Boehner could deliver the 217 House votes he needed to cut a deal. He could shut down the government and risk default, but because of hard-line conservatives, Boehner couldn’t pass anything. House Minority Leader Nancy Pelosi (D-Calif.) told Obama and Reid this privately, and she repeated it publicly. This belief drove the Democrats throughout the crisis: stand firm and Boehner will be forced to fold.

(WATCH: Nancy Pelosi blasts GOP for budget saga)

But they had to keep each other in check.

Reid nixed an idea in mid-September to invite the congressional leaders over to the White House for a talk. It sends the wrong message, Reid argued to Obama in a call. We shouldn’t even create the appearance of a negotiation, Reid said.

The meeting never happened.

In the House, Boehner and his leadership team ran through a spate of options — none of which his conference would accept. First, the Ohio Republican proposed keeping the debt limit and government-funding discussions separate, which Democrats were privately hoping would happen. He suggested passing a budget bill that completely funded the Affordable Care Act. A resolution would be passed alongside that defunded the law, but it could’ve been stripped out by the Senate and sent to Obama’s desk.

The proposal was dubbed the “Cantor plan,” after House Majority Leader Eric Cantor (R-Va.), who came up with the idea. Then, Boehner would’ve had Republicans fight hard on the debt ceiling, using the sequester as a bargaining chip against Obama.

(Also on POLITICO: Mitch McConnell defends deal, slams Obamacare tactics)

But that’s where Boehner miscalculated: he assumed House Republicans only wanted a show vote. Instead, they wanted so much more, determined to nullify the health care law and use a government shutdown and threat of a debt-limit default to get there.

Boehner’s rank-and-file were being egged on Sen. Ted Cruz (R-Texas), a populist freshman who was quickly gaining followers in the House as quickly as he was alienating his fellow Republicans senators.

In the run-up to the shutdown, Obama was weak politically; his Syria strategy was panned by both parties; Obamacare was suffering poor poll numbers; and Republicans thought they had him on the ropes.

(WATCH: Timeline of Ted Cruz’s Obamacare crusade)

Yet Cruz’s anti-Obamacare drive played right into Democratic hands.

“The president gets up every day and reads the newspaper and thanks God that Ted Cruz is in the United States Senate,” a Republican senator pointedly told Cruz at a closed-door meeting.

Even amiable and soft-spoken Republicans like John Boozman of Arkansas tore apart Cruz in a private GOP meeting, saying he was making GOP senators seem like they were for Obamacare when they had fought so hard to torpedo it. Boozman pointedly told Cruz he hadn’t been bullied since middle school, and he wouldn’t be bullied now.

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