Romney may have beaten Santorum on Tuesday night, but he’s already running against Obama.

But that might not be enough to help Romney. Mitt Romney needs to improve his lot with swing voters, and right now the polls suggest he's in the worst position of any candidate since Bill Clinton in 1992. Fifty-two percent of independent voters view Romney unfavorably, and only 35 percent view him favorably, according to a recent Washington Post poll. President Obama has a 50-46 favorable-to-unfavorable rating with independents. Among women, a key voting bloc, Obama has an 18 point lead over Romney in a recent USA Today/Gallup poll. Republican presidential candidates usually do worse with female voters, but this is suitcase-on-the-front-lawn bad.

And women aren’t the only bad news for Mitt. A CNN survey showed Obama leading Romney 54 percent to 43 percent nationally, up five points from February. In the Gallup swing-state poll, he is up 51 to 42 over Romney.

How does Romney fix all of this? He can pray that Obama stumbles and the economy stops improving. Another way is to mount some kind of Clinton-like comeback. That would require a set of political pirouettes that Mitt Romney has never shown the legs for. He lacks Bill Clinton's raw political skill, and he also lacks Clinton’s biography. In 1992, the Clinton team could re-introduce the Arkansas governor as the son of a single mom from modest roots. Romney appears scared of patches of his biography. His wife seems great, but so did Elizabeth Dole and Tipper Gore, who were also called on to bedazzle voters into overcoming their doubts about their husbands.

Romney has another hurdle: He can’t take advantage of the ideological flexibility that allows primary candidates to refashion themselves as general election candidates because he has already shifted on everything from abortion to his status as a Republican to his advocacy for gay rights.

All candidates try to shed the pointed views they held during the primaries or at least downplay them. In 2008, Obama's top economic adviser Austan Goolsbee quietly told a Canadian official that his boss was merely posturing when he promised to renegotiate the North American Free Trade Agreement, that it was just talk to rile up the base and he didn't really mean it. The Obama team had to insist he'd never do such a thing. Of course, as Goolsbee predicted, Obama never followed through on his primary campaign rhetoric.

Romney can’t do this. The press and the Democrats have him so pinned down, an aide can't say “Etch A Sketch” without having it become the new symbol for Romney's lack of core convictions. When Ann Romney said she was going to "unzip the real Romney," and introduce him to Americans, it threatened to animate this storyline again. 

The president called out Romney by name Tuesday in his critique of Paul Ryan’s budget, a continuation of Joe Biden’s effort the week before to tie the front-runner to the Republican Congress. As Ezra Klein points out, Romney has tried to stay vague on the details of his proposals, and Obama is trying to staple Romney to the highly detailed plan that he has endorsed. If, as the nominee, Romney tries to suggest he might do something different from Ryan while still supporting it—as he did last year with the congressman’s aggressive plan for restructuring Medicare—the Obama campaign will pounce. What normally might be seen as a garden-variety political act of “flexibility” might quickly be seen as another example of Romney’s lack of core convictions.

While Mitt Romney was moving on to the general election, Rick Santorum’s campaign announced that he would campaign in Pennsylvania ahead of the April 24 primary. “We have now reached the point where it's halftime," Santorum said. "Half the delegates in this process have been selected, and who's ready to charge out of the locker room in Pennsylvania for a strong second half?" He’s not going anywhere, was the message. That’s certainly been true in a growing string of primaries where Santorum hasn’t been able to break out of his box. Since his revival in the Colorado, Minnesota, and Missouri contests on Feb. 7, Santorum has not been able to win support beyond the most conservative wing of the GOP. As Ron Brownstein noted recently, Santorum’s support has been confined to a narrow band of evangelical voters who identify themselves as conservatives.