At last night’s debate, there were surprisingly few direct attacks on Mitt Romney. This morning, Newt Gingrich and Rick Santorum finally went after him, but neither was able to land a knockout punch:

Santorum began the morning’s attacks, accusing Romney of abandoning Republicans in Massachusetts by “bailing” from a difficult 2006 reelection campaign. When Romney cast his decision not to run for a second term as a selfless choice – saying he engaged in politics as a “citizen,” not a longtime official – Gingrich pounced. …

But the bad blood between Romney and his foes resurfaced before the debate was out, as Gingrich again went on the offensive – this time accusing Romney of duplicity in distancing himself from negative ads run by a super PAC funded by his “millionaire friends.”

Romney once more avoided a deer-in-the-headlights moment, though his speech was uncharacteristically halting as he explained that he wouldn’t support any attack ads that were inaccurate.

Romney’s response to Gingrich’s attack on a pro-Romney super PAC was mystifying – he first said he never saw the PAC’s anti-Gingrich ad, and then went on to recite it blow-by-blow. But he managed to keep his composure,and came out of the dustup without any serious damage.

The question many observers have been asking is why are Romney’s rivals treating him so lightly? At the Daily Caller, Matt Lewis raises an interesting possibility:

Some of the candidates, by now, know they cannot win. As such, they have little incentive to attack Romney. (Perhaps he will give them a position in his administration if they help him? — Why ruin that? Or maybe he would counter-attack them and make them look bad if they criticize him? …. Or maybe they just want to be thought of as “nice”?)

Meanwhile, the candidates who think they can win — Rick Santorum and Newt Gingrich — probably believe their best shot at the nomination is to finish second in New Hampshire. And while going “negative” in a debate may hurt Romney, it would also tarnish their reputation, as well.

Lewis’s take makes sense. Perry isn’t hitting Romney because his past attempts to do so have blown up in his face (the convoluted “flip-flop” attack, for example). Whether Perry’s staying in the race because he actually believes he can compete seriously in South Carolina, or whether he’s simply to redeem his national reputation after multiple embarrassments, he has little incentive to go after Romney. The possibility of a future appointment may not even factor into the equation.

As for Huntsman and Paul – could they really be pulling punches with Romney because they’re gunning for administration positions? There’s notoriously bad blood between Huntsman and Romney, and Paul doesn’t have a shot at an appointment.

But at least Huntsman isn’t afraid of sparring with Romney once in awhile. Paul’s unwillingness to attack the frontrunner is actually the most confounding out of all of the candidates. He actually turned down an opportunity to criticize Romney this morning when it was explicitly presented to him. Paul’s polling second in New Hampshire, so why is he spending his time punching down at Santorum and Gingrich, who are both polling at single digits? It makes no sense.

Beyond that, Santorum and Gingrich are going to have to start turning their guns on each other at some point soon. Gingrich is fading in South Carolina, but not fast enough that Santorum can rest easy. Meanwhile, Gingrich can’t allow Santorum’s recent burst of popularity to propel him to the top of the polls there. Of course both of them have to attack Romney – they’re locked in a three-man race with him in South Carolina right now – but one of them will also have to definitively capture the not-Romney title. That means they’ll have to take the gloves off pronto – and with Santorum’s recent fundraising boost and Gingrich’s $5 million cash infusion, they now have the money to do it.