We finally will get a debate tonight with all the current Republican presidential candidates. There are lots of debates this fall, but I suspect interest will wane as time goes on. Given the tussle with the president over scheduling and the debut of Texas Gov. Rick Perry, the audience for tonight’s face-off is likely to be very large. That said, no one debate is necessarily determinative, but it certainly can sink a candidate — as Tim Pawlenty found out when he whiffed the chance to confront Mitt Romney over “ObamneyCare.”

For Perry the stakes are high indeed. The public, media and donors are trying to figure out whether there is substance or just slogans. Does he seem presidential? Can he take a punch? After Romney’s speech yesterday Perry’s staff sent out a pro forma shot, arguing: “As Governor of Massachusetts, Mitt Romney failed to create a pro-jobs environment and failed to institute many of the reforms he now claims to support.” Romney’s obvious response is that for a governor of a deep blue state, he didn’t do so bad and, by the way, where are Perry’s ideas? In fact Perry is arguing for his candidacy without many specific proposals, simply relying on his tenure as governor. But that’s not going to satisfy the voters, especially in early states that demand clear answers to their queries. Perry will also be expected to tell voters whether he still believes in some extreme ideas in his book (abolishing Social Security, repealing the 16th Amendment, etc.).

Romney, on the other hand, has to defend himself against charges that he is insufficiently faithful to the hard-core base. (If he were honest and fearless, he’d say that anyone who caters excessively to the base, likely isn’t electable.) But he is more likely to point to elements in his record as governor, the substance of his proposals and his private-sector experience. As for job creation, arguably only he and Hermann Cain have ever actually created private sector jobs. Can he demonstrate that he’s better positioned to win the general election and that he’s more up to speed on the critical issues we face? He’ll need to make that case, and, yes throw a counterpunch or two when Perry challenges his conservative bona fides.

Rep. Michele Bachmann (R-Minn.) can get back in the race with a forceful attack on Perry’s conservative bona fides on marriage, immigration and HillaryCare (which he once cheered for). Moreover, she’d gain some traction, I suspect, if she picks up on Sarah Palin’s crony capitalism and directly applies it to Perry, who has richly rewarded donors with cushy jobs and set up some slushy tech funds to hand out cash to connected businessmen. In essence, she needs to make a convincing case that Perry talks a good game but doesn’t embody and practice the principles of the Tea Party. If she can do that, I suspect she can climb back in the race and make Iowa competitive again.

Bachmann may get a helping hand from Rick Santorum, who also needs to knock Perry down a peg or two. Santorum will certainly bring up mandatory HPV vaccinations, which Perry championed until he entered the presidential race. He’ll give Perry a hard time on his changing position on the 10th Amendment and gay marriage. And, given his interest and experience in foreign policy, especially with regard to Iran, you might see him challenge Perry on those grounds as well.

It’s far from clear that any other candidate has the ability to climb into the top tier. However, Rep. Ron Paul (R-Tex.) may join the Perry pile-on, while Jon Huntsman may attack Romney for his Massachusetts record. Paul has credibility (undeserved I would argue) with Republican audiences, so he may be the wild card in all this.

It should be an entertaining event. If Perry isn’t bloodied, he will be pleased. If he his, expect more attacks by his rivals. The next few months are do-or-die time for all the candidates.