Believe it or not, it’s debate night again, 9 p.m. kickoff, on Fox News Channel, live from Orlando. Yesterday I taped some discussion of the outlook for the debate with Fox Business News, and excerpts of that interview are airing throughout the day.

To quote Yogi Berra, “It gets late early out there,” in that despite the fact that we’re in late September, and have about five weeks to the filing deadline in South Carolina (which would officially set the field) and about four months and change until the Iowa caucuses (though that could change), the window of opportunity is closing for most of the candidates in the field.

In most polls, both nationally and in the early key primary states, it is a two-man race between Rick Perry and Mitt Romney. Before the last debate, the conventional wisdom was that Michele Bachmann needed to have a dramatic, aggressive performance to get the spotlight back on herself and to take Perry down a peg. Her tough criticism of Perry’s Gardasil decision and stance on illegal immigration appeared to do that . . . until her infamous suggestion later in the evening that Gardasil could cause mental retardation, which may have done irreparable damage to her candidacy. As recently as August 9, she was less than two percentage points behind Rick Perry in the RealClearPolitics polling average. Today she has slipped behind Ron Paul, trails Mitt Romney by about 13 percentage points, and trails Perry by more than 20 percentage points.

Tonight, she faces the same challenge, with the bar set even higher: she needs to crack the foundation of Perry’s support while avoiding any criticism or charge that makes her appear loose with the facts, reckless, or out of the mainstream.

Perry’s past debate performances haven’t been bad enough to hurt him significantly, but he’s actually lost a little ground in the polls in the past two weeks. Some have wondered if Perry’s back surgery from the summer has left him with lingering fatigue issues; his performances in the debates’ first halves have been significantly better than his second halves.

Perry can serve up red meat with the best of them, but the question is what else he can do, and whether he seems like a man capable of building a national consensus to move national policies in a conservative direction. As Rich put it, “to become president of the United States, he’ll have to reach persuadables who don’t value outrageousness for its own sake. If he’s never willing to back down, he’ll have to go — should he win the nomination — all the way to November 2012 defending the notion that Federal Reserve Chairman Ben Bernanke is possibly guilty of treason.” From what the Texas governor has shown so far, a Perry presidency would leave the country with the cultural standoff of the Bush years — much whining and carping from the usual corners about the reckless, dumb cowboy Texan running roughshod in the White House. While many Republicans would like their nominee to wear that criticism as a badge of honor, others would prefer a nominee who can demonstrate a style of national leadership distinct from Bush’s. What’s more, Perry may face more criticism on Gardasil and will almost certainly face withering criticism that his policies amount to amnesty, and perhaps that too many of the jobs created in Texas during Perry’s reign have gone to illegal immigrants.

Romney finds himself in a position that ordinarily would cause some candidates to panic, but he and his team seem pretty confident that they’re playing the long game the right way. He still leads New Hampshire by a wide margin, is a strong second everywhere, and still matches up quite well against Obama in the head-to-head polling. From this, Romney may try to argue that Perry isn’t electable, but it’s not so clear that a lot of Republican primary voters want to hear that message this early. With Obama looking so weak at the moment, the argument that “your proposals are right on the merits but don’t poll well” won’t fly with grassroots conservatives eager to see the government shift dramatically to the right on January 20, 2013.

For former New Mexico governor Gary Johnson, tonight is a big night, with his national television debut.* He brings a more libertarian view on most issues, and will likely echo Ron Paul on foreign policy and drug legalization if the topic is raised. Johnson might be an interesting test of whether the collection of views we might call “Ron Paul-ism” works better or worse without Ron Paul himself.

For everyone else, the opportunities to break out of the background are diminishing. Newt Gingrich will probably pound the moderators and make some good arguments, but his energetic, pugnacious debate performances just haven’t translated into poll strength or even donations, it would seem. Herman Cain has won a lot of fans with his affable performance in past debates, but he appears to have seen his breakout moment come and go. (For one, brief, shining moment, Cain was second in the RealClearPolitics average: June 27, 2011.) Rick Santorum, too, has shown occasional moments of energy and passion in the debates, but he’s still struggling to hit 5 percent in Iowa, a state that should be his bread-and-butter. Jon Huntsman had an awful appearance in the last debate, and would be well advised to avoid the corny jokes or trying-too-hard cultural references. With 10 percent in New Hampshire, it’s not unthinkable that Huntsman could end up having a bigger impact on this race in the near future, but he still faces a steep uphill climb.

* UPDATE: In the comments, a reader contends that Johnson’s inclusion in the Greenville, South Carolina, debate back on May 5 constitutes his “debut,” although that debate featured a very limited field of Tim Pawlenty, Paul, Santorum, Cain and Johnson — no Romney, no Bachmann, no Perry, no Gingrich. (At the time, Sarah Palin, Donald Trump, Mike Huckabee and Mitch Daniels were also being mentioned as likely candidates).

That debate had 3.2 million viewers; by contrast, the debate on Fox News Channel in August had 5.1 million viewers. For perspective, last night Bill O’Reilly had 3.26 million viewers.