8 p.m. ET on CNBC, it’s the end of the primary world as we know it — I think. The fourth GOP debate is set for November 10th, less than two weeks from now, so it’s possible we’ll end up with the same group of 10 onstage for that one as for this one. But I doubt it. For one thing, the 2.5 percent polling threshold that Fox has set for the next debate is sufficiently high that Chris Christie would miss it if it were held today and Kasich would be right on the bubble. Maybe they’ll both have a solid debate tonight and get a bounce … or, more likely, they’ll both be afterthoughts as voters begin to consolidate behind the five or six top-tier candidates.

Beyond the polling requirements, though, there’s a sense among some righties that it’s time to trim some of the dead wood to leave more time at the next debate for the serious contenders. At a minimum, the never-gonna-wins like Graham, Pataki, and Gilmore should be dispatched and “undercard debate” canceled. Arguably so should the potentially formidable but as yet tractionless candidates like Christie, Paul, and Jindal. It’d be painful to boot them offstage while the field is unsettled, though; what if Jeb finally throws in the towel and his centrist supporters start sniffing around Christie or Kasich as a second choice? Do you want to push them out of the spotlight at the moment voters might finally be giving them a second look? Do you want to boot Jindal before he’s had so much as a single chance to compete on the main stage? On the other hand, how long do guys who are within the margin of error of zero in national polls get to soak up airtime? If I were running Fox, I’d split the remaining field into two groups of five, with the first, lower-polling group set for 7:30 ET — a better time slot than the 6 p.m. dinner hour tonight’s undercard is getting — for 90 minutes and then go right into the main event of Trump, Carson, Rubio, Cruz, and whoever’s in fifth at 9 p.m. for two hours.

But all of that’s in the future. The other reason not to try to thin the herd at the next debate is because the herd might thin itself first. If Bush disappears tonight and Rubio shines, that may be the last strike for Jeb among the donor class. If you’re a grassroots conservative salivating at the thought of the prince flaming out of the race despite having had a mountain of money dumped on him, tonight’s your night to see it happen in real time. The guy seems so miserable about this long, humiliating slog, waiting in vain for Trump to fade and watching his former apprentice Rubio inch past him in the polls, that maybe he’ll treat a so-so debate performance as an escape hatch. I can’t even imagine what his strategy to win might be. If he gets angry, it’ll reek of him trying to manufacture “energy”; if he doesn’t, he’ll probably get lost in the shuffle. Maybe the Bushes will finally put aside their family pride and let the poor guy go home. Also on the chopping block tonight: Rand Paul, another candidate who seems conspicuously miserable running and is under pressure from his pal Mitch McConnell to focus on his Senate seat so that Republicans retain their majority. He’s one Cruz bounce away from accepting that the “conservatarian” vote isn’t going his way, which means he may have no choice tonight but to attack his “friend” Ted as a phony libertarian. That’s awfully risky given how it’ll anger some of the grassroots righties whose votes he needs for Senate, but if he’s serious about this presidential run, I don’t think he has a choice anymore. If he lays off Cruz tonight, that’s a sign that he’d rather lose the presidential primary than gamble his Senate seat to win.

Who’s the biggest target tonight, though? It’s not Jeb. He’s done such a fine job blowing himself up, there’s really no reason for anyone onstage to bomb him. At this point, Trump pounding on him might actually create sympathy for him. The big target’s probably not Trump either. He’s been taking punches for four months and no one except the soft-spoken Carson has topped him in the polls. Attacking him seems pointless. Is … Carson the big target? He’s a target, especially for Cruz, who needs to clear Carson out of his way among evangelicals in Iowa. But you can’t hit Carson too hard; beating up on the nicest guy onstage looks so bad, even Trump will probably pull his punches. Which means the big target tonight, in all likelihood, is Marco Rubio. Jeb has a strong incentive to hit him, as Rubio’s getting admiring looks from the donors and voters Bush needs. Trump has an incentive to hit him, as Rubio’s obviously a more serious threat long-term than Carson is. Cruz arguably has an incentive to hit him if he believes, as many people do, that this race will eventually turn into a Rubio/Cruz death match. And Fiorina has an incentive to hit him, as Rubio’s probably the main beneficiary in the polls of her slow fade from the media spotlight after the last debate. Trump will hit him on amnesty, Bush will hit him on inexperience (we’ll see if he uses the “Republican Obama” line), Cruz will hit him on failing to stand up to the GOP leadership, and Fiorina will hit him on lord knows what — maybe his missed Senate votes. If there’s going to be a pile-on tonight, it’ll be on Rubio. But in risk, there’s opportunity: If Rubio’s well prepared for the attacks, which he will be, and comes out looking good, that’s all the more reason for donors to decide that he’s their best option going forward, not Jeb. Rubio can effectively finish Bush tonight depending on how clutch he is under pressure. And both candidates know it.

Only one thing is certain: If Trump screws up, he’s going to whine and whine and whine.

https://twitter.com/realDonaldTrump/status/659382468332511232

Here’s your thread to comment. Two new ads to entertain you while we wait, both of them, er, “outside the box.”

Update: Well, here’s a bit of mystery via Rick Wilson.

Man oh man, the dumb, pre-planned move a certain campaign is about to make in the big debate is campaign-ending stupid.

— Rick Wilson (@TheRickWilson) October 28, 2015

A Twitter pal wonders if the “pre-planned move” will involve Jeb demanding that Rubio resign his Senate seat due to low-ish attendance lately. That seems plausible — Bush has been grousing about that on the stump lately and that Sun-Sentinel editorial yesterday made the issue more timely. Jeb’s Super PAC launched a (groan) Twitter account today designed to needle Rubio about missing votes. It’s a lame attack and Rubio will surely be ready for it, but it’s all Bush may have now.