Republican front-runner Donald Trump will face his three remaining challengers – and his nemesis in the media, Fox News’s Megyn Kelly – on Thursday evening in Detroit in the 11th GOP presidential debate.

The debate begins at 9 p.m. Eastern time on Fox News Channel.

It comes at a crucial point in this entirely unexpected GOP primary. Trump dominated the primaries of “Super Tuesday” this week, and now he has a significant lead over his top rival, Sen. Ted Cruz, R-Texas, in the race for Republican convention delegates.

But in a divided field, Trump has still won less than half of all the delegates awarded so far. That leaves his opponents with a viable – but risky and destructive – strategy. The only way to stop Trump from winning the Republican nomination may be to stop anyone from winning it: dividing up the delegates so that no one has a majority.

Then, the theory goes, the party would head into a chaotic, divided convention – the first true “floor fight” for any party in decades – and hope that a candidate other than Trump would emerge.

For Trump’s rivals, the next step in that battle will come Thursday.

The front-runner is likely to come under furious attack from Cruz and Sen. Marco Rubio , Fla., who have sought to portray Trump as a “con artist” hoodwinking voters with promises he can’t keep. They frequently mention “Trump University,” which was not a school but a series of real-estate seminars, and now is the subject of three lawsuits in which students say Trump bilked them with misleading promises.

Both Rubio and Cruz had given Trump a pass for months before turning on him at the last debate a week ago. A few days later, on “Super Tuesday,” Rubio said that those last-minute attacks had worked, and that they had cut into Trump’s leads in places like Virginia.

The problem was that Trump still won Virginia. And six other states.

Cruz, by contrast, won three of the states up for grabs that night. Rubio won just one.

In Thursday’s debate, Trump will most likely also be confronted with the words of the last GOP nominee, former Massachusetts governor Mitt Romney. In a speech in Utah on Thursday morning, Romney was expected to echo the attacks of Rubio and Cruz and label Trump a fraud.

“Donald Trump is a phony, a fraud,” Romney will say, according to a speech prepared for delivery Thursday morning at the University of Utah’s Hinckley Institute of Politics. “His promises are as worthless as a degree from Trump University. He’s playing the American public for suckers: He gets a free ride to the White House, and all we get is a lousy hat.”

In recent days, Trump has hit back against both of his top challengers, calling Rubio a “little senator” and calling Cruz a liar. He has also dismissed Romney, blaming him for the GOP’s 2012 loss to President Obama.

In Thursday’s debate, Trump will also face Kelly, one of the three moderators. In the first GOP debate in August, Kelly had asked Trump a question about his past unpleasant comments about women: “How will you answer the charge from Hillary Clinton, who was likely to be the Democratic nominee, that you are part of the war on women?”

Trump answered the question: “What I say is what I say. And honestly Megyn, if you don’t like it, I’m sorry. I’ve been very nice to you, although I could probably maybe not be, based on the way you have treated me. But I wouldn’t do that.”

Afterward, Trump complained that the question was too harsh, and seemed to blame it on Kelly’s menstrual cycle. “You could see there was blood coming out of her eyes, blood coming out of her wherever,” Trump said. The next time Fox News hosted a debate, in Iowa, Kelly was again a moderator – but Trump boycotted the event, holding a fundraiser for veterans’ charities instead.

In the lead-up to this debate, Kelly told the Associated Press that she believed Trump – now a veteran candidate – was better prepared for the hard questions of a presidential debate.

“I think at this point in the game he understands better how these things go. He knows he can handle me. He can handle any interviewer,” she said.

Also in the debate will be Ohio Gov. John Kasich, a relative moderate whose best showings in this primary season have been second-place finishes in New England states: Massachusetts, Vermont and New Hampshire.

In the last debate, Kasich did not participate in the attacks on Trump.

Instead, he seemed to be holding his own private event at the side of the stage, ignoring the fighting next to him and trying to speak directly to voters. “Shoot for the stars. America’s great, and you can do it,” he said in his opening statement.

Now, however, Kasich is under increasing pressure to fight or flee the race.

Kasich’s best hope for the nomination was that he could win Midwestern states like Ohio and Michigan, and begin a last-minute comeback. But now, polls show him trailing badly in Michigan, where Trump is leading with the Republican primary looming March 8. One recent poll showed Kasich losing to Trump even in his own home state, which will hold its vital, winner-take-all primary March 15.

If Kasich wants to win those states, he may have to enter the fray against Trump.

If Kasich doesn’t want to enter the fray, he may come under increasing pressure from other Republicans to drop out so that his voters might flow to another Trump challenger.

This will be the first GOP debate without retired neurosurgeon Ben Carson, who said Wednesday that he did not see a “path forward” for his campaign. Carson – a Christian conservative who last year briefly challenged Trump for the lead in national GOP polls – has not yet formally suspended his campaign.

Instead, he said he would not attend Thursday’s debate. Then, on Friday, Carson will make a speech about his future at the Conservative Political Action Conference, a major gathering of conservatives at a hotel in the Maryland suburbs of Washington.

Carson’s departure may not change the dynamics of the GOP race much: He has won a total of eight delegates, far behind Trump’s 319.

But it will change the Republican debates, where Carson had been the anti-Trump: a low-key, cheerful presence on a stage full of big, loud egos. He didn’t fit, and was often proud to point that out.

“I’m . . . the only one to operate on babies while they were still in a mother’s womb, the only one to take out half of a brain,” he said in the first GOP debate, in one of the most memorable lines of the primary season. “Although you would think, if you go to Washington, that someone had beat me to it.”

For those who remain in the race, there is no time for mistakes: This is the most vital two weeks of their campaign so far.

The next states to vote will be Kansas, Kentucky, Louisiana and Maine, all on Saturday. After that, the next primaries will be March 8, when Republicans vote in Hawaii, Michigan, Mississippi and Idaho.

(c) 2016, The Washington Post