The second Republican presidential debate starts at 8 p.m. ET on CNN — and it’s set to run, no joke, for nearly three farking hours. If you’re playing a debate drinking game, for the love of Mike, pace yourself. And don’t include mentions of Reagan as a cause to drink in this one: Although always a staple of candidate rhetoric, tributes to the great man will be even more common than usual since the debate’s being held at the Reagan Library in Simi Valley. The good news is that that’s a golden opportunity for the more conservative candidates in the field to pressure Trump on his deviations from Reaganesque conservative orthodoxy. (Except Ted Cruz, of course, who’s still playing the role of Trump’s deferential little sidekick for strategic reasons.) The bad news is that Trump’s got an easy comeback for that. For all of Reagan’s admirable qualities, we’re past the point where we can afford to emulate him on immigration, no?

In an alternate universe, this debate would be a fascinating clash of personas and credentials. In this universe, it’s mainly an exercise in seeing if anyone can take Trump down a peg, including Trump. Jake Tapper and new Trump nemesis Hugh Hewitt are among the moderators so expect challenging, substantive policy questions. In theory, Trump could whiff so badly on one that he blows up his candidacy on the spot; in reality, he seems to have no trouble BSing his way through tough interviews with promises that his policy will be terrific, whatever that policy might end up being. There’s really no way for him to whiff among the people who like him: For them, the right answer is pretty much whatever answer Trump chooses to give. The threat to him tonight isn’t a policy misstep, it’s that Ben Carson and Carly Fiorina might make another good impression on GOP voters who are still getting to know them, possibly aided by Trump himself deciding to get a bit too nasty with them. I’d go so far as to say that if Carson has a solid debate, he’ll lead in at least one poll next week no matter what Trump does tonight. We’ll see.

The dirty little secret of this debate is that for all the drama surrounding Trump and whether Carson can continue his rise, it’s more likely to matter in hindsight as a moment that effectively ended the campaigns of some of the marginal candidates in the race. Trump and Carson will both be fine next week but Chris Christie, say, might not be. If he disappears tonight, it might be the last time he’s featured in a primetime 2016 event. Rand Paul’s another guy in trouble: His favorable ratings took a dive after the first debate, either because viewers didn’t like his NSA answer or didn’t like him jabbing at Trump. Rand’s going to double down on the latter strategy, a risky move for a guy who’s tried to build an anti-establishment brand by questioning Republican orthodoxy. Once upon a time, Paul was angling to be the populist in the race; now he’ll be leading the charge on TV against the noisiest Republican populist in America. If his favorables slip further afterward there’s probably no coming back. Same goes for Scott Walker. Unlike Paul, he’s still well liked by Republican voters and kinda sorta has a chance to return to the top tier based on his record, but how much more would you want to gamble on Walker’s chances if he has another dull debate? Especially if Marco Rubio, the other supposedly electable center-righty in the race, turns in his usual solid performance by comparison.

Which brings us to Jeb. He may have the most to lose this evening:

Five-plus months before the first ballots are cast, Bush faces the kind of do-or-die moment most top-tier candidates confront far later in the primary process – a chance to revive a campaign that has shattered fundraising records, but sunk as low as 6 percent in recent national polls.

Bush, one former adviser to his father said, “needs to show he’s the tough-minded guy we know he is.” If he doesn’t, the former aide added, “Well, you know, it might be over.”

The Bush campaign privately thinks Bush’s slow-burning fuse – evidenced on the golf course and in sometimes-testy debate sessions – has at long last been lit. But the biggest fear, expressed by Bush allies, donors and party operatives to POLITICO, is that another lousy debate performance will precipitate an exodus of the big money ($100 million-plus in super PAC and campaign cash so far) that has kept the former Florida governor afloat despite his dismal poll numbers.

If Bush craps the bed again, the donor class may decide that Rubio’s the last best hope of establishmentarians to get an electable candidate as nominee. Jeb will be spoiling for a fight to show how “high energy” he is, which is why, if I were Trump, I’d ignore him as much as possible. Starve him of any easy opportunity to show off one of the counterattacks he’s been preparing. If he insists on hitting Trump, let him instigate the attack so that it looks like the establishment’s boy is picking a fight with the populist, not merely defending himself. Trump’s supposedly toying with “toning down” his act a little, and he’s showing more discipline on the trail lately now that he feels he has a chance to win. Here’s a chance to demonstrate that. Or, alternately, he could unleash some new insult on Jeb that Bush isn’t prepared for, leave him looking totally flummoxed and outwitted, and end up destroying Bush’s candidacy that way. Either/or. Whatever the strategy, Bush needs to make something happen to protect his lead in the “invisible primary.” Otherwise it might be Rubio time, or — shudder — Mitt Romney time.

Here’s your thread to comment. Exit question: Why did Trump initially demand that CNN donate the advertising proceeds of tonight’s debate to charity as a condition of him appearing? After the astounding amounts of free media they’ve given him over the past few weeks, showing up is the least he could do to say thank you.