Noam Scheiber thinks a narrow Romney loss won’t mean very much:

Which leaves two probable scenarios: Either a single-digit Romney loss or a single-digit Romney win. If it’s the former, the GOP establishment will no doubt wake up on February 29 with persistent indigestion. But it’ll just be a slightly more advanced form of the same malady they’ve been suffering since South Carolina. I doubt it’ll be acute enough for them to want to blow things up and place all their chips on the next Rick Perry (which is to say, an untested candidate who looks good on paper but could easily self-destruct). In that case, we’re almost certainly still looking at a long, ugly slog to the nomination for Romney.

Naturally, I agree that Romney will press on to win the nomination one way or another. A loss in Michigan would be embarrassing, but it would be easy for his campaign to explain the loss by pointing to Romney’s unusual boasting about his rejection of the auto industry bailout. Let’s remember that Romney won Michigan four years ago by engaging in the most pathetic pandering of the last two cycles, and he’s not doing that this time. On the other hand, ABC reports that a Michigan loss for Romney will cause a lot more than persistent indigestion:

A prominent Republican senator just told me that if Romney can’t win in Michigan, the Republican Party needs to go back to the drawing board and convince somebody new to get into the race.

“If Romney cannot win Michigan, we need a new candidate,” said the senator, who has not endorsed anyone and requested anonymity.

The senator believes Romney will ultimately win in Michigan but says he will publicly call for the party to find a new candidate if he does not.

The name mentioned for this role is Jeb Bush, who happens to be the one fantasy candidate who has repeatedly stated that he has absolutely no intention of running. Would any of the fantasy candidates respond favorably to a desperate plea from just one Republican Senator? I doubt it. Would a public call for a new candidate by a “prominent” national Republican trigger a mass exodus of Romney supporters? That also seems unlikely. Think about what is being proposed here. This “prominent Republican Senator” doesn’t think Santorum or Gingrich has a chance, but he thinks a nominee selected by party leaders out of desperation would be more competitive than the candidate who has already been at this for years? How many pro-Romney Republicans would go along with this? My guess is that quite a few of them would be alienated and demoralized.