Mitt Romney’s biggest vulnerabilies in the GOP presidential race are supposed to be threefold: his moderate past, the health-care bill he signed into law as Massachusetts governor, and his record at Bain Capital.

And on all three counts, he basically got a pass at Monday’s debate.

In fact, the words “health care,” “moderate” and “liberal” didn’t come up once in reference to Romney.

The Myrtle Beach debate was characterized by some awkward moments for Romney, and many saw it as perhaps his weakest debate performance so far. Specifically, he got a little flustered when it came to negative ads a pro-Romney super PAC is running, whether he would release his tax returns and even felon voting rights.

But if those were stumbles, Romney was in no danger of losing his footing.

“Republican voters are locking in for Romney. The questions are about his competence, character and commitment to Republican and conservative values,” said GOP strategist Dan Hazelwood. “No candidate even challenged those credentials.”

View Photo Gallery: The five remaining GOP presidential candidates faced off Monday night in a debate in Myrtle Beach, S.C.

As with the dozen-plus earlier debates, the former Massachusetts governor came out of Monday’s debate looking like the Teflon man.

The totality of the debates have been marked by a striking lack of traction from his opponents on issues that should, by all rights, be difficult for Romney to cope with.

Yet more often than not, they aren’t even being mentioned.

That was particrularly the case on Monday, when Romney’s health-care bill didn’t even come up, and there was only a glancing reference to his more moderate (some say socially liberal) past. The latter came from a regular citizen who submitted a question, not one of Romney’s opponents.

Even when it comes to Bain, Newt Gingrich was arguably more on the defensive than Romney. The former House speaker at the outset of the debate was pressed on his earlier contention that he wouldn’t attack his fellow Republican opponents. From there, Romney gave a perfunctory explanation of how Bain took over companies and in some cases laid people off, and the debate moved on.

So why aren’t Romney’s opponents beating the drum when it comes to these three issues? And why are we talking about felon voting rights instead?

It appears Romney’s opponents are simply trying to open up new fronts with which to attack him.

The old ones are still there and are still being reinforced in ads, but given that none of them has done much to damage his frontrunner veneer, this is about throwing stuff at the wall and hoping it sticks.

Already, Romney’s foes appear to have gotten some traction on the super PAC issue and his tax return, with the candidate having to confront both issues today and saying now that he’ll release his latest return this spring. But given that won’t likely happen until the GOP race is in effect over, that probably won’t be of much help to any of his Republican opponents.

On felon voting rights, former Pennsylvania senator Rick Santorum appeared to lay a trap for Romney, getting him to say he opposed felon voting rights and then noting that he did nothing to change the fact that felons who serve their sentences are returned to the voter rolls in Massachusetts.

But on that issue and the super PAC ads, we have to wonder how many people are really going to care about such things. Felon voting rights aren’t exactly front-of-mind right now, and explaining the intricacies of campaign finance law to people is a pretty boring venture.

“Tax returns, super PAC issues and felon voting rights won’t move Romney’s numbers,” said GOP pollster Jon Lerner. “However, that doesn’t mean last night’s debate was without impact.”

Lerner noted that Gingrich did himself a service with his performance and could turn himself into the Romney alternative in the race.

But Hazelwood said the nature of the attacks will do little to unseat Romney even if that one-on-one race comes to pass.

“Process and irrelevant and esoteric issues don’t unseat a juggernaut,” Hazelwood said. “If these were preconceived plans, they should rank up there with the French hiding behind the Maginot Line in 1940. A recipe for disaster.”

With all three of these newer lines of attack, there is little to suggest they will move the needle that much. But the name of the game right now is to shake the unshakable.

Which is why we’re talking about felon voting rights today.