Rep. Michele Bachmann (R- Minn.),Texas Gov. Rick Perry, Herman Cain and Newt Gingrich all attempted to attack Mitt Romney from the right. Each of these candidates proved to be too flawed to weather scrutiny when he or she climbed into contention. And arguably none did a particularly good job of drilling down on Romney’s past deviations from conservative orthodoxy. The challenge for Rick Santorum, arguably the sole survivor of the not-Romney set, is to do what they could not. There are, I would suggest, five questions that are key to assessing whether Santorum can prevail.

First: Can Santorum make the case that RomneyCare is a disqualifier? His communications director yesterday sent out a release arguing: “As Governor Tim Pawlenty so aptly said, RomneyCare should be called ObamneyCare. Everyone knows that Governor Romney’s top-down, government-run mandated health insurance plan was the basis of ObamaCare. Oddly enough, the only accomplishment that Gov. Romney points to and actually defends during his tenure as Governor — is the most liberal, the most intrusive and unconstitutional.” He continued: “In fact, the only area that conservatives would appreciate Romney flip-flopping on would be Romneycare. So why he doubles down on this liberal accomplishment instead of just flip-flopping as usual is beyond me. We’re all looking for Gov. Romney to finally have firm conviction on something, but it’s pretty telling that he picks Romneycare.”

Romney would, of course, dispute that this is his only accomplishment (and no one has yet made a serious case that RomneyCare, a state measure, is unconstitutional), but the real issue is whether voters who practically all know that RomneyCare contained an individual mandate will now turn against him because of it. So far, RomneyCare has not been the silver bullet Romney’s opponents believed it to be, in large part because the economy became the central issue in the race.

There is reason to believe that the mere existence of RomneyCare will not in and of itself bring down the front-runner. If Santorum, however, can make the larger point that Romney will not pursue conservative initiatives or will compromise too readily with Democrats, he may be able to raise more doubts about Romney among conservative and very conservative voters.

Second: Can Santorum convince Republican voters he can actually win the nomination? In the most recent Washington Post-ABC News poll not even 1 percent of GOP voters think Santorum will be the nominee. If he is to change that perception he will need to start winning contests, and deliver speeches and conduct interviews in which he projects confidence, optimism (about his own prospects and the country’s) and command of the issues. He’s got to do this in a likeable way, which means he can’t spend all his time savaging his opponent.

Third: Can Santorum overcome Romney’s advantages in money and organization? As the race spreads out to multiple states, some of which are in expensive media markets, Santorum will have to fund paid ads and work to get positive earned media coverage. He’ll need to put out a get-out-the-vote operation and find some effective surrogates. He won’t have the benefit of a debate until late this month. And if Romney sweeps most of the races on Super Tuesday, it’s quite possible he’ll severely limit the number of debates, thereby depriving Santorum of critical visibility.

Fourth: Can Santorum convince Republican primary voters that he is more than “just a social conservative”? Many, if not most, primary voters haven’t heard him lay out his economic agenda, don’t know how he proposes to cut spending and aren’t familiar with his tax plan. He may feel as though he’s explained all that hundreds of times, but with each new group of states there are voters who are focusing on the race seriously for the first time. And many voters who have been tuned in really didn’t focus on Santorum. Unless they understand Santorum’s economic message, like it more than Romney’s and are convinced it is an effective contrast to President Obama’s vision, he’ll have a hard time weaning voters from Romney. So long as GOP voters are under the impression that he cares most about and knows most about social issues, he’ll have a hard time convincing them that he can effectively go up against Obama in an election focused on the economy.

And finally: Can Santorum deflect the argument that he’s a “big-government conservative,”that is, not the consistent conservative he claims to be? There are certainly some clunkers in his record from the point of view of conservatives: votes for Medicare Part D and No Child Left behind and opposition to right-to-work legislation. He’ll need a credible and forceful explanation for why those positions shouldn’t be held against him or aren’t critical to evaluating his candidacy.

This sounds like a lot. And it is. The right made a critical error in not recognizing Santorum’s strengths earlier in the race. But time is not his greatest enemy, and it’s not useful for him to dwell on why conservative pundits went chasing after defective contenders. What he now has to do is grow in stature, project himself as Romney’s equal and convince conservatives that they can not only improve their chances of winning back the White House but also get a more consistent conservative if they jump from the Romney ship.

It’s not an easy task, but the good news for Santorum is that the Republican electorate seems especially susceptible to impressive debate performance, feisty rhetoric and bold attacks on Obama. Santorum will need to do all that and more. But if anyone in the GOP field (past or present) can do it, Santorum’s the guy.