To some observers, Mitt Romney's new ad, aimed at Iowa Republicans, seems to be saying, "Yes, I'm Mormon. But at least I'm not a philanderer. Like Newt."

As such, it carries considerable risks. Not only by reminding conservative evangelicals that he belongs to a religion many do not approve of, but also by taking on Gingrich - subtly, perhaps, but unmistakably -on his three marriages and past person indiscretions.

One Gingrich adviser told ABC News that the ad "is basically Romney saying 'My family is better than your family.' It's going to backfire."

The Gingrich adviser says that as long as Gingrich is honest about his past failings, voters will focus more on candidate attributes dealing with leadership and the economy. Around 50%of American marriages end in divorce, the adviser pointed out.

But the issue could have resonance with the Iowa conservative base, because Gingrich has not just a failed couple marriages under his belt; there are and have been myriad allegations of behavior that these voters would view as immoral.

Romney earned the enmity of many of his fellow GOP candidates during his 2008 run for his sharp attacks on his rivals. Throughout these last few months, he has generally held his fire as he enjoyed his frontrunner status, but with this new challenge from Gingrich has come a new sharply aggressive approach from Camp Romney in Boston.

In yet another Romney attack - this one a far more direct fire - the Romney campaign this morning will hold a conference call in which former New Hampshire Governor John Sununu will attack Gingrich as unreliable and untrustworthy.

Gingrich and his campaign seem to be eagerly awaiting this attack. "Sununu doesn't like Gingrich because Newt wouldn't go along with his deal to raise taxes in the 1990 budget deal," a Gingrich adviser tells ABC News.

Indeed, when Sununu was White House chief of staff for President George H.W. Bush, he now claims he thought Gingrich had agreed to the deal and reneged. Gingrich denies that account, but more to the point, this gives Gingrich an opportunity to remind Republican voters that he rebelled against Bush Sr.'s budget deal, which included tax increases.

Gingrich advisers say the question today becomes: "Did Mitt Romney support raising taxes in the 1990 budget deal?"

Throw me into the Sununu Briar Patch, they say.

-Jake Tapper