President Obama’s decision to block the Keystone XL pipeline puts in perspective the misstep by House Republicans at the close of the year. It’s hard to even remember the rotten reviews House Republicans got for initially refusing and then agreeing to the Senate’s two-month payroll tax cut extension. But the Republicans did keep language forcing the president to make a decision on the project before November, and his rejection is being greeted with glee by Republicans.

Mitt Romney put out a statement that reads: “President Obama’s decision to reject the Keystone XL crude oil pipeline is as shocking as it is revealing. It shows a President who once again has put politics ahead of sound policy. If Americans want to understand why unemployment in the United States has been stuck above 8 percent for the longest stretch since the Great Depression, decisions like this one are the place to begin. By declaring that the Keystone pipeline is not in the ‘national interest,’ the President demonstrates a lack of seriousness about bringing down unemployment, restoring economic growth, and achieving energy independence. He seems to have confused the national interest with his own interest in pleasing the environmentalists in his political base.”

A number of House and Senate Republicans have released similar statements. Senate Minority Leader Mitch McConnell (R-Ky.) said:. “Keystone was an obvious choice: everybody in Washington says they want more American jobs now. Well, here’s the single largest shovel-ready project in America — ready to go. Some of the news outlets are calling this pipeline controversial — I have absolutely no idea why. The labor unions like it. Democrats want it. It strengthens our national security by decreasing the amount of oil we get from unfriendly countries. And it wouldn’t cost the taxpayers a dime. . . . The only thing standing between thousands of American workers, and the good jobs this project will provide is President Obama.”

One thing you can say for the South Carolina primary: It has woken up Mitt Romney. In Spartanburg, Romney went on a tear:

Romney is often accused of having no core beliefs. But in fact, when he talks in defense of the “profit motive” and defends risk takers, he is, to a greater degree than we usually see, speaking from conviction.

Pundits can construct any crazy argument, I suppose. Some even suggest it would be better for Mitt Romney to lose in South Carolina and get toughened up in the process. Well, let’s be frank: Winning is always better than losing in politics.

So it’s not surprising that Mitt Romney is stepping up the pace against Newt Gingrich, who had a strong debate outing Monday and has another chance on Thursday. The race has almost certainly tightened, as evidenced by a concerted offensive by the Romney camp against Gingrich

In a pair of new ads, the Romney team goes back to Republicans who served with Gingrich in the House, making the point that he’s a disaster in a leadership position. Here is the first, featuring former Sen. Jim Talent:

A similar ad with former New York congresswoman Susan Molinari is posted as well. Both also held a press conference call to make the case that Gingrich will throw conservatism under the bus (e.g. attacking Rep. Paul Ryan on Medicare and going after private equity companies) to advance himself.

I asked the Romney campaign for its reaction to Gingrich’s latest attacks on Bain (“explotive,” Gingrich dubbed it). Communications director Gail Gitcho replied, “Speaker Gingrich continues to prove that he is an unreliable conservative leader. Newt Gingrich and Debbie Wasserman Schultz are reading from the same talking points. His campaign tactic is interesting to watch, but it’s not going to work.”

Among Newt Gingrich’s more disingenuous statements in the debate this week was his claim that he had not been attacking Bain or capitalism, just asking questions. That’s nonsense, of course.He was the one who accused Mitt Romney of “looting” firms. It is his super PAC that is running the “King of Bain,” which is replete with misrepresentations and distortions. And sure enough, when he was safely away from the debate stage yesterday he went at it again.

He proclaimed: “The Bain model was to go in at a very low price, borrow an immense amount of money, pay Bain a great deal of money and leave. Now, I’ll let you decide if that’s really good capitalism. I think it’s exploitative. It’s think it’s not defensible.” That does not even pass the straight-face test for a description of what private equity firms do.

He speaks in generalities and invectives because, as we have seen in the “King of Bain” examples, there aren’t really specific cases that support that cartoon version of what private equity firms do.

Rick Santorum has a challenge. He doesn’t need to catch Mitt Romney, but it would certainly help his cause to come in ahead of Newt Gingrich, who is vying for the not-Romney spot. Right now his poll numbers in South Carolina are troubling to his supporters. In the RealClearPolitics average he is tied in South Carolina with Rep. Ron Paul (R-Tex.) in fourth place with 14.3 percent. In Florida he’s in third, but more than 25 points back in the RCP average.

Meanwhile, Gingrich’s debate performance gave him a lift, and he has one more shot on Thursday to seal the deal with the voters. So what can Santorum do?