Santorum can spoil Romney nomination clinch (The New Republic) Last week Nate Silver wondered how much better Rick Santorum would be doing in the GOP primaries if Newt Gingrich had been on the sidelines the whole time. Using data from the polling firm PPP, Silver assumed Santorum would have received about 57 percent of Gingrich's votes, Mitt Romney 27 percent, and Ron Paul 16. The punchline: It would undoubtedly still help Mr. Santorum if Mr. Gingrich dropped out -- especially if Mr. Gingrich endorsed Mr. Santorum and asked his delegates to vote for him. In fact, the combined total of Santorum and Gingrich delegates right now is quite similar to the number that we calculate Mr. Santorum would have won without Mr. Gingrich in the race. But that would be just the first step for Mr. Santorum -- at best, a necessary but not sufficient condition for a comeback. He'll need to find some further means by which he can eat into Mr. Romney's coalition, and he'll need to do so in a hurry since 21 states have already voted. This sounds about right to me. And there really isn't a scenario, short of Romney rethinking this whole presidency fixation of his, by which Santorum could actually overtake him. But it's not crazy to think Santorum can sufficiently "eat into Mr. Romney's coalition," as Silver puts it, to deny Romney the 1144 delegates he needs to lock up the nomination. The "further means" Silver alludes to is actually quite straight-forward: a major jolt of giddiness on the part of conservatives who believe Romney may finally be beatable. Special Section: Election 2012 Santorum opens wide lead over Romney in Pa. I'm not talking about ordinary momentum here -- the kind you get when you win Iowa in a crowded field and get a bump heading into New Hampshire. I'm talking about a paradigm-shifting change in which we move from the world we've been living in for the past year-and-a-half, in which Mitt Romney has remained the inevitable nominee no matter how much he struggles, to a world in which it's suddenly possible for him to fall short. If Newt drops out following Santorum's big wins in Mississippi and Alabama, I think the world could change in precisely this way. Of course, for Santorum to stuff Romney as a practical matter, he'd have to pick up a series of big wins starting next week with Illinois (where he's currently only a few points behind Romney), then in states like Wisconsin (where he's comfortably ahead), Texas (which looks good for him without Newt in the race according to this recent poll) and California (which is presumably the toughest of the four). I think he could afford to lose New York and New Jersey, but not many more big states beyond that. But this no longer seems so out of the question. Take Illinois, where the FiveThirtyEight polling index has Romney at 38.7 percent, Santorum at 34.5 and Gingrich at 14.1. Using the PPP allocation of Gingrich support to the other candidates, a Gingrich departure (formal or in spirit) would leave Romney and Santorum tied at 42.5. Now, obviously Illinois is a big state with an enormously expensive media market, which would play to Romney's strength (i.e., his wallet). And there's always the possibly that Gingrich dropping out will have the opposite effect of the one I imagine -- it could focus the mind of the GOP rank-and-file on the need to fall-in line behind Romney or risk a Goldwater-esque defeat. But if I'm right, and the shift to a Romney-Santorum race turns out to be invigorating for conservatives, Santorum may be about to open up a pretty big lead in Illinois. And if he gets on a roll, even California could start to look winnable before long. At present, the RealClearPolitics polling average there has Romney at 33.8, Santorum at 25.3, and Gingrich at 15.3. Allocating the Gingrich support according to the PPP model leaves Romney at 38 and Santorum at 34, a margin that seems eminently closeable when you throw in the secret post-Newt, paradigm-shifting giddiness sauce. Am I getting ahead of myself? And there's no doubt that one of the most persistent features of this nomination contest has been the distinct lack of momentum from one state to the next. Still, the whole point of a paradigm-shift is that the old rules no longer apply. If we really are in a different world now, the scenario I'm spinning out is entirely possible. Of course, even under that scenario, Romney would arrive at the convention with the most delegates, and the GOP elders would be inclined to hand him the nomination. So in some cosmic sense this exercise may be moot (except insofar as failing to clinch the nomination before the convention would be a stunning display of weakness). But, then, if we get to a convention without a formal winner, who at that point will feel confident predicting much of anything? Noam Scheiber is a senior editor at The New Republic, where he writes about politics and Obama administration economic policy.