At some point, television is going to have to start limiting which Republican candidates get invited to the debates. The herd of hopefuls must be thinned. This may happen soon, and tonight may be the last of the mega-debates of the season. One can only hope.

Of course, the Republican field is somewhat self-thinning itself already. Tim Pawlenty dropped out early, after realizing the only people he had on board were media pundits who had declared he'd be a dandy candidate. Republican voters didn't agree, and Pawlenty was smart enough to realize it sooner, rather than later.

Just today, a candidate most people (even most people who pay attention to this sort of thing) weren't even aware was running dropped out as well. Representative Thad McCotter announced he had been marginalized so much that he didn't have a prayer of winning. He had a telling quote while making this announcement: "If they keep you out of the debates, you are out of the conversation and you can't run. It was sort of 'death by media'." McCotter dropped out to concentrate more on his re-election to the House, it seems.

But other Republicans don't have this kind of pressure. Many of the presidential candidates aren't running for any other office, and the ones with time (and money) to burn can stay in as long as they like, no matter what the polls say. However, the media doesn't have to indulge what amounts to "vanity campaigns" forever, and the likelihood is that the closer we get to the actual voting (which is roughly four months from now), fewer candidates are going to be invited to the nationally-broadcast debates.

The first two of these to go are likely to be Rick Santorum and Jon Huntsman. Santorum has been doing the far-right thing much longer than the Tea Party ever existed, but he has not yet caught fire (or even been noticed, much) among Republican base voters. He regularly pulls about 2-3 percent in national polling, and will probably be the first to go.

Huntsman may stick around a bit longer, because (much like Pawlenty), the media seem to love him. "He's an ideal candidate!" they enthusiastically gush, and the Republican voters answer back, "No, he's not!" with equal frequency. In the past month of polling, Huntsman has not gotten above two percent. Sooner or later, the media's going to have to break off their crush on Huntsman, and forget to mail his invitation to the next debate round.

The next tier of candidates might stick around a bit longer, but barring any sort of surge in the polls, none of them has much of a chance at this point. Michele Bachmann had her day in the sun, and has been eclipsed by Rick Perry. Bachmann's numbers have collapsed from their highs, and now regularly polls in the single digits. Rick Perry, for better or worse, is now the officially anointed Tea Party candidate, much to Bachmann's annoyance.

Herman Cain, of course, has already walked the path Bachmann now trods. He was the flavor-of-the-month for a while (after being deemed winner of one of the first debates), but his numbers have also sank back to single-digit territory (his highest number in the past month has been seven percent). Cain presents an interesting dilemma, however, being a black Republican. While he is going to deserve being kicked out of the debates right after Huntsman and Santorum (based on their respective poll numbers), the networks may allow him to stick around longer so they won't seem to be biased in any way. This isn't going to do the Republican Party any good at the polls with African-American voters, however, as they will once again overwhelmingly go for Obama next fall.

Newt Gingrich is also polling worse than Bachmann. He did chart one poll at 10 percent, but it was likely a fluke (he hasn't hit double numbers since June). Newt has always been in the race just to sell books and have a good time at the debates, so once he is disinvited from the stage, watch for him to quickly fade from everyone's view.

The last of the second-tier candidates is Ron Paul, who may manage to hold on longer than the rest of the pack. He's the only one out of this group who has shown poll numbers which are (slightly) rising during the past month or so, and he's charted three polls (out of seven) in the last two weeks in double-digits, even hitting 13 percent in one of them. Paul may continue to slowly pick up support, especially if the other candidates start disappearing from the debates. Protest votes by Republicans not enamored of the top two candidates may decide Ron Paul is worth a second look, after their first choice fades, in other words.

The two candidates accorded "frontrunner" status are going to be the real story tonight, of course. Rick Perry has shot up to 25-30 percent in the polls after jumping in the race late, but he may be losing steam. His debate performances so far have shown voters that he can say outrageous things and get away with them, but that this doesn't exactly endear him to the moderate voters he's going to need if he stands any chance of beating Obama next year. Mitt Romney is attempting to fight his way back to the front of the pack, after being eclipsed by Perry getting in the race. But Romney's numbers have been turning upwards over the past few weeks, and he seems to be regaining some of the voters who abandoned him for Perry initially.

But whatever the outcome of tonight's debate, the news will likely center on the Perry/Romney matchup. And, unless Sarah Palin surprises everyone by jumping in the race, these two are likely going to be the real "horserace" story on the Republican side until the primaries actually start. Sooner or later, television executives are going to realize that having too many people on the stage is detracting from the serious business of hearing from the people who actually stand a chance of winning the party nomination. Sooner or later, the Republican herd (at least on primetime television debates) is going to need to be thinned out.

-- Chris Weigant

Follow Chris on Twitter: @ChrisWeigant