A week ago he said, “I believe with all my heart that the winner of the Florida primary next Tuesday will be the nominee of the Republican Party.” Are we now still looking at a three- or four-man race, splitting anti-Trump votes on the right, even if Trump cleans up tonight? Good lord. I haven’t felt this much queasiness and dread since … four minutes ago, when I found out they’re making a new Indiana Jones movie.

Skip to 3:20 below for the key bit. Consensus opinion on social media is that he’s just putting on a brave face ahead of a humiliating loss in order to encourage his fans in Florida to turn out today, but I don’t know. For one thing, he says at one point that none of the candidates is on pace to reach 1,237 delegates, which of course isn’t true. Trump is, although whether he remains on pace depends heavily on tonight. Maybe Rubio’s in deep denial. Or maybe not: There’s a school of thought out there that Cruz can’t stop Trump head to head even if he starts winning consistently. He’d have to win big, over and over, in one proportional state after another to hold Trump below the margins he needs to clinch. (Although, again, that depends on how well Trump does tonight.) Could be that Rubio’s decided to hang around if Kasich loses Ohio and drops out purely in the interest of denying Trump some extra votes and holding his delegate share down. Except … that makes no sense, since he’d surely hold Cruz’s share down even further. Either that or so many righty voters will abandon Rubio after tonight that he’d end up as a Carson-esque four-percenter, barely affecting either Trump or Cruz. Donors will cut him loose and he’ll end up an afterthought in the race. He has no incentive to put himself through that.

Or does he? Here’s a quirk in the RNC rules that I was unaware of until this week. I thought that once a candidate had won a delegate, that delegate was pledged to him on the first ballot at the convention regardless of whether he was still in the race or not. Not so, per former RNC counsel Ben Ginsberg:

In the first presidential roll call vote at the convention, a rule in effect for the first time in 2016 automatically binds more than 90 percent of delegates to specific candidates based on those delegates’ statewide votes. That leaves only a very small pool of delegates that Trump could win over in order to reach a majority on the first ballot: 166 delegates who are already unbound, plus an unknown number whose state laws will unbind them if their candidate drops out by the time of the convention. (There are currently 12 of these delegates, but, importantly, that number will increase if one of the current candidates drops out. For example, should Marco Rubio drop out without winning any additional delegates, 152 delegates would be added to the unbound pool, nearly doubling the number available to Trump’s powers of persuasion to gain a first-ballot majority.)

Once Rubio is out, “Rubio delegates” become free agents, even on the first ballot. If Trump gets to Cleveland needing fewer than 152 delegates to clinch, those delegates could make the difference. Maybe Rubio, who’s getting verrrrry close to joining #NeverTrump, will formally remain in the race even if he stops campaigning so that he continues to “control” those delegates at least on the first ballot, ensuring that Trump can’t win until the second. And once we reach the second, many of Trump’s own delegates will become unbound free agents themselves, potentially forcing him to win over a lot more than 152 to clinch. Just something to think about this week, in case Rubio endorses Cruz and urges his voters to support him but never actually formally suspends his campaign. In that case, he may simply be playing keepaway with the delegates he’s already earned. (Alternately, the RNC Rules Committee could change the rules so that every candidate’s delegates are bound to him on the first ballot whether he’s still in the race or not. But they won’t meet for several months; until then, staying in is Rubio’s only option.)

Incidentally, if you want to know why Rubio performed so far below expectations this year, this graph is as good an explanation as any:

Here's how badly the GOP "Establishment" is getting its ass kicked: pic.twitter.com/jHYRSSOF98

— Dave Wasserman (@Redistrict) March 15, 2016

Rubio and Kasich have piled up many more endorsements than Trump and Cruz have, but go figure that those wouldn’t matter in a campaign dominated by populist voters.

Whatever happens this week, there’s zero doubt that Rubio’s speech tonight will be the most suspenseful of any candidate’s. He might drop out, or he might not; he might endorse Cruz, or he might not; he might deliver a full-throated, eloquent case for “Never Trump!” like he did three days ago, or he might not; and he might be speaking at a moment when Trump is all but clinching the nomination with strong performances in Illinois or Missouri, or he might not. I think he’ll stay low key tonight so that he’s not accused of sour grapes and then say his piece about Cruz and Trump later this week, but I don’t know. He may never again have the same amount of media attention that he’ll have five hours from now. If he wants his campaign to “die with dignity,” as Benjy Sarlin put it, this may be the moment.