Romney’s chances now depend on his ability to stop that from happening. He needs Bachmann, Perry and Santorum to pick up as many Cain supporters as possible, so that his conservative opposition remains fragmented. He needs the other candidates to step up their attacks, calling into question Gingrich’s conservative bona fides. And, above all, Romney needs to start winning over at least some of that reluctant 75 percent of the GOP electorate.

The only way he will do so is if those voters conclude that Gingrich is unelectable. There is ample evidence to make that case. With Gingrich as the nominee, one Romney adviser told me, the election will become a race about yesterday instead of tomorrow. It will be about his tumultuous speakership rather than Obama’s failed presidency. That’s not the kind of race you want to run, Team Romney says.

For now, the Romney campaign is leaving that argument to others. But it may not be able to do so for long. Romney strategists liken the campaign to an Indy 500 race — you drive steady, let the other cars rub metal and spin out, and make sure you are there in the last lap. The problem is, you need eventually to rub some metal yourself, and to make a move if want to cross the finish line first. Today, with Gingrich surging, Cain’s supporters up for grabs and Iowa caucuses less than a month away, the time to make that move is running out.