(Eric Thayer/Getty Images)

Analysis

Four years after Democrats waited on superdelegates to settle an unsettled race, Republicans are waiting for their Superman - and waiting, and waiting.

That waiting is threatening to overcome a race that has party elders increasingly concerned about their ability to defeat a vulnerable President Obama. Suddenly, the panic button is in reach - and there may be nothing any of the current candidates can do to stop it from being pressed.

A loss by Mitt Romney in Michigan would unleash years' worth of frustrations at the GOP frontrunner. It might even be enough to convince a critical mass of Republican leaders to look outside the current field, to a non-candidate who could consolidate the party at that extinct political animal known as a contested convention.

"If Romney cannot win Michigan, we need a new candidate," a veteran GOP senator who hasn't made an endorsement in the race told ABC's Jonathan Karl late last week.

Romney remains the favorite for the nomination, and would still be so even if he loses Michigan. But a string of losses that start in Michigan would make a Rick Santorum win plausible - something that would spark serious worry among Republicans whose primary goal is winning the presidency.

The concerns inside the party about the two candidates most likely to win the nomination are different, but both speak to the Republican Party's identity crisis this election year.

The unease over Romney starts with a passion gap and spills over into electability. Romney continues to look vulnerable, notwithstanding the fact that he holds an advantage in every objective campaign metric, in addition to a delegate lead over his rivals.

Six years of campaigning for the presidency haven't been able to convince the party's regulars to fall in love with Romney.

But a loss in Michigan would betray more than a simple lack of enthusiasm. He'd be losing a large industrial Midwestern battleground - filled with the kinds of voters who will decide the presidential campaign - not to mention the state he was born and raised in, and where his father was governor.

The man he's in danger of losing to brings his own set of problems in the minds of many Republicans. Rick Santorum's rise has been fueled by a blue-collar economic appeal, in addition to his strong stands on conservative social issues.

It's the latter that is getting the scrutiny now, and would be made famous by Democrats in the fall. Santorum's positions on abortion, gay rights, and even contraception are coming into focus early, in a preview of a fall campaign that has some Republicans worried about a Goldwater-like blowout.

Republicans don't want to nominate someone they believe is likely to lose. That will leave them reexamining their choices if Romney doesn't close out Santorum next Tuesday in Michigan, and follow with a dominating performance a week later on Super Tuesday.

This dynamic could lead to yet another chance for Newt Gingrich. But the fact that he's blown several previous campaign moments, coupled with his lack of campaign discipline, leaves him as damaged goods, too.

That's what leads to talk of another candidate. Prominent Republicans who haven't endorsed in the presidential race - former Florida Gov. Jeb Bush, Indiana Gov. Mitch Daniels, and yes, even former Alaska Gov. Sarah Palin - would be among those who could face pleadings from party regulars about a late, late entry.

It's too late for such a candidate to run through the front door. If a candidate were able to qualify for every primary whose filing deadline hasn't passed, he or she could be a candidate in only 11 states worth 482 convention delegates - less than half the total needed to clinch the nomination.

The only possibility left for a non-candidate, then, would be a contested convention. To the extent that powerbrokers hold sway, that could leave things swinging back to Romney, particularly if he enters with a strong plurality that's just short of a majority.

But these would be uncharted waters in an unstable year. Romney desperately hopes that Republicans don't dip anything more than a toe.