"In the span of just two weeks, Mitt Romney has gone from seeming quite vulnerable to the near-inevitable Republican nominee."

Nate Silver says, noting that since December 13, Romney's gone from 42% to 72% at Intrade, and opining that even 72% seems low. (Here's the Intrade chart, and you can see that Romney's just back where he was before, following a brief plunge. Meanwhile, here's what happened to Newt.)

Can you visualize a scenario in which Romney does not emerge as the winner? Silver tries. He notes that Romney's numbers are low for a frontrunner, and you can tell that plenty of Republicans still resist him. Yes, but what could happen? He might do poorly in Iowa. Silver's numbers show that Romney might get as much as 36% in Iowa, but "as little as 8 percent, which could drop him all the way down to fifth or sixth place."

Even a third-place finish in Iowa, much less something worse, might now be viewed as disappointing for Mr. Romney, increasing the risk of either a loss in New Hampshire or a close call that made Mr. Romney vulnerable heading into South Carolina and Florida....

My view is that the probability of these scenarios is higher than is generally acknowledged.... [but] there’s still that issue of one of the other candidates actually having to defeat him. One of the more likely scenarios is that Mr. Romney does take some bruises in the early states, whether at the expense of Mr. Gingrich, Mr. Perry, Mr. Huntsman or even Mr. Paul. But then the other candidate runs out of steam. Mr. Romney recovers and wins, perhaps after a strong performance in Michigan on Feb. 28, on Super Tuesday.