The four Republican presidential candidates will face off Thursday night at a moment both crucial and surreal – their last debate before the winner-take-all primaries in Ohio and Florida.

The debate, held at the University of Miami, will be broadcast at 8:30 p.m. Eastern time on CNN.

The center of attention will once again be billionaire front-runner Donald Trump, who in the last debate reassured the audience – without being asked – that “there is no problem” with the size of his fingers, or his manhood.

That odd moment hasn’t seemed to hurt him. In fact, Trump has won five of the eight states that have held GOP contests since then. He has now won 15 states, and has accumulated about 458 Republican delegates, which is 99 more than his closest rival, Texas Sen. Ted Cruz. Trump needs 1,237 delegates to win the nomination.

Instead, the GOP electorate has turned to devour the candidate who insulted Trump’s fingers.

Florida Sen. Marco Rubio, who had launched a series of Trump-style attacks on the front-runner – mocking his hands and his tan, now finds himself in a dreadful slump at the worst possible time. In all four states that voted Tuesday, Rubio finished so far behind that he was awarded zero delegates for the night.

Now, Rubio is trailing Trump badly, even in Rubio’s own home state – Florida, which will award all 99 of its delegates to the winner of Tuesday’s primary.

If Rubio loses there, it would be a devastating blow not just to his presidential campaign but his political career. Rubio is leaving the Senate, and he would have to face the next phase of his life with Trump’s epithet “Little Marco” metaphorically hung around his neck.

On Wednesday, as his supporters fretted, Rubio conceded his efforts to out-Trump Trump had backfired – and diminished Rubio himself instead.

“In terms of things that have to do with personal stuff, yeah, at the end of the day it’s not something I’m entirely proud of,” Rubio said in a “town hall” on MSNBC. “My kids were embarrassed by it, and if I had to do it again, I wouldn’t.”

On Thursday night, Rubio will have to decide whether to continue on the attack against Trump – but in more genteel terms – or whether to abstain, try to rebuild his gravitas, and make a personal plea to his home-state voters.

But other candidates smell weakness, so Rubio will undoubtedly face new attacks.

In addition to Trump, who should relish a chance to mock Rubio’s slumping poll numbers, Cruz should also be on the offensive. Cruz believes he can beat Trump in a two-man race, so both the candidate and a pro-Cruz super PAC have been hammering Rubio in Florida, hoping that a loss there will get Rubio out of the race entirely.

The fourth candidate onstage will be Ohio Gov. John Kasich, who has tried to stay out of the fighting between Trump, Rubio and Cruz. For now, Kasich’s above-it-all strategy seems to have worked better than Rubio’s: polls show Kasich actually in a close race with Trump in his home state of Ohio.

On Tuesday, Ohio will be almost as big a prize as Florida, with 66 delegates for the winner and zero for everybody else. In Ohio, Kasich has the state’s GOP apparatus strongly behind him, and a fairly high approval rating. If he can beat Trump anywhere, this is it.

Because of that, Kasich may have a hard time staying out of a fight with the front-runner on Thursday night. Already, Trump has been calling him “an absentee governor” for spending so much time on the campaign trail, according to news reports.

Trump himself may also face new questions about his recent tax returns – which he has refused to release – and the true size of his wealth.

A recent report in Crain’s New York Business showed that Trump had received a tax break from New York state, which is only available to couples with an annual income of $500,000 or less. Trump’s campaign manager told Crain’s that this was an error by the state.

Trump will also likely face questions about the physical violence used against protesters at his rallies, which Trump has seemed to encourage from the stage. The latest violence came to light on Thursday, when videos seemed to show a protester – already being led out of a rally by men in uniform – being punched in the face by a Trump supporter as he passed.

“The shock of it all is starting to set in,” Rakeem Jones, the man who was hit, told The Washington Post in a telephone interview. “This dude really hit me, and they let him get away with it. I was basically in police custody and got hit.”

Trump could also face questions about the alleged behavior of his campaign manager, Corey Lewandowski, after Trump’s post-primary press conference Tuesday. A Washington Post reporter witnessed Lewandowski roughly grab the arm of a reporter for Breitbart – a conservative news outlet generally friendly to the front-runner – as the Breitbart reporter tried to ask another question while Trump made his exit.

Breitbart chief executive Larry Solov later issued a statement saying that “It’s obviously unacceptable that someone crossed a line and made physical contact with our reporter.” But the statement did not say with certainty that Lewandowski was the person who had done the grabbing.

(c) 2016, The Washington Post · David A. Fahrenthold