Tomorrow evening the Republican presidential candidates will face off in Iowa for the first of two debates (the second on Dec. 15). The debate may not turn into a high-octane battle between Newt Gingrich and Mitt Romney, but given the renewed focus on the Iowa caucuses, there is a good chance one or more of the candidates will challenge Gingrich, perhaps even trying to provoke him into a testy outburst.

Rep. Ron Paul (R-Tex.) and Romney have both been taking shots in advance of the debate, making the case that Gingrich is neither consistent nor conservative. For both of these candidates the name of the game is to narrow Gingrich’s lead and make Gingrich’s premature pronouncement (that he has not only the Iowa caucuses but also the nomination in the bag) look like typical Newt egomania. Paul relishes being the heavy and has no problem gruffly rebuking his rivals, as he did with Texas Gov. Rick Perry on taxes in a prior debate. Watch for him to push Gingrich on spending, subsidies and special-interest group lobbying (which Gingrich insists he never did).

Romney’s task is a bit tricker. His appeal rests in large part in being the calm executive, not the provocateur. I suspect he’ll be leery of initiating an attack on Gingrich but will be more than ready to punch back, as he previously did by reminding the audience that Gingrich was a fan of the individual mandate. He will surely hit his big theme: He’s a steady businessman with concrete answers to solve the country’s problems. Implicit in that is the argument that Gingrich isn’t steady, has made his livelihood in and around government and has many pie-in-the-sky ideas but few specific proposals that can be implemented. Romney is also going to remind voters, no doubt, of his lovely wife and family. That would be his only wife.

Gingrich surely knows that everyone else on the stage will have an incentive to go after him. His favorite stunt — filibustering a question by arguing with the moderator — isn’t going to work as well now that he’s the front-runner. He’ll need to restrain his instinct to condescend to his rivals and to adhere to positions that simply aren’t credible. If the conversation is about hiring kids as janitors or denying that he “lobbied” for Freddie Mac, it won’t be a good outing for him.

Gingrich will also need to respond to the central critique against him on policy grounds: He is not a small-government conservative. It doesn’t help him when the New York Times’s David Brooks writes: “Gingrich loves government more than I do. He has no Hayekian modesty to restrain his faith in statist endeavor. For example, he has called for ‘a massive new program to build a permanent lunar colony to exploit the Moon’s resources.’ He has suggested that ‘a mirror system in space could provide the light equivalent of many full moons so that there would be no need for nighttime lighting of the highways.’ I’m for national greatness conservatism, but this is a little too great.” It’s a problem when his opponents can honestly say “Gingrich’s to the left of David Brooks.”

Gingrich is especially vulnerable to attack as a big-government cheerleader from Paul, Texas Gov. Rick Perry, Rep. Michele Bachmann (R-Minn.) and Rick Santorum, who are far more in tune with the Tea Party sensibility. Frankly, all of the candidates, including Romney, have been more specific on critical fiscal issues (e.g., debt reduction, entitlement reform) than Gingrich has. And no candidate comes close to the number of schemes, projects, initiatives and subsidies that Gingrich has favored over the years. It’s not going to fly for him to argue his grand ideas aren’t explainable in a debate format. (When being tarred as a extravagant statist, it is best not to say, “My ideas are so grand and extensive I couldn’t fit them into a mere debate.”)

The debate is an opportunity, one of a final few, for Perry, Bachmann and Santorum to show they can compete in and beyond Iowa. Arguably, only one of them will come out of Iowa with a viable campaign. That would require placing ahead of the other two and coming within shouting distance of the third-place finisher. All three will need to make the case, as they have in prior debates, interviews and ads, that they are more consistently conservative than Gingrich is on abortion, stem cell research, spending, regulation, global warming, TARP, Freddie Mac and Fannie Mae and federalism. All three (and Romney, too) will no doubt take issue with his stance on illegal immigration, although it’s not likely to be a topic on which Perry wants to engage.

We shouldn’t forget the moderators, of course. They can raise topics that Gingrich’s competitors probably don’t want to. Does he recall that many Republicans voted to fine him for violating House ethics rules? What about current and former members of Congress who recall him lobbying them face to face? Is he serious about having elementary school children work as janitors? Since he got rolled by Bill Clinton in the government shutdown, why wouldn’t he be outfoxed by Democrats once again? Why is he still making book sale appearances, and is that really appropriate in a presidential race?

As we know from prior debates, it is often the counterpunch that stings the most. Candidates risk losing points with the audience by being overly aggressive. That said, I suspect that at times the gloves will come off and the moderators will be only too happy to spark some conflict.