On top of the polls and riding a wave of momentum from his strong performance at Saturday night's ABC-Des Moines Register debate, Newt Gingrich is now the clear front-runner for the GOP nomination. And, for the first time this year, the "steady as she goes" Mitt Romney campaign looks off-balance.

Even so, the consensus among the handful of top Republican strategists whom I reached out to Sunday was that Romney remained the odds-on favorite for the nomination.

The biggest reason: Gingrich himself.

As one long-time Republican put it, Gingrich "can self-destruct on a dime." Another wrote in an email, "Newt would truly be changed if he didn't mess this up."

That said, Gingrich has time on his side. Between now and the Iowa caucuses Jan. 3, there is one more debate and then a dead zone of at least a few days around Christmas. A compressed window means fewer chances to make a big mistake or for the weight of his baggage to catch up with him.

Most agree that Romney can't simply wait for Gingrich to self-destruct, but they also acknowledge that the Romney campaign has few good options.

Said another Republican strategist, who acknowledged he was "very concerned" about Gingrich's chances to win the nomination, "there's very little that Romney can do now to stop Newt that will accrue to Romney's benefit. "

Romney's greatest assets, his steadiness and "sobriety," as Romney put it himself at the debate the other night, are not enough for a GOP electorate that wants to be energized and maybe even a little tipsy with enthusiasm for the nominee.

The risk for Romney is that if he falls back into traditional campaign tactics, such as grainy attack ads, he looks like the kind of " typical politician" that GOP voters say they don't want. Even his strategy of rolling out endorsements from elected officials in key primary states, as he's doing today in New Hampshire, just "makes him look more establishment," one Republican strategist said.

Romney has spent most of the year as the presumptive nominee and over-dog. We now get to see how he responds to being the guy chasing instead of leading.