(CNN) In the first post-Super Tuesday Republican presidential debate, Donald Trump enters as the dominant front-runner, and Ted Cruz and Marco Rubio will once again try to slow his momentum.

Trump emerged from March 1 stronger than ever in his quest for the White House, notching seven victories and growing his delegate count. For both Cruz and Rubio, the window to slow Trump's rise is closing, particularly as the GOP race moves ahead to large states with winner-take-all delegates.

The prime-time event, hosted by Fox News in Detroit, also comes as the anti-Trump movement among Republicans is belatedly beginning to gain steam, including with the 2012 candidate, Mitt Romney, who is set to give a speech attacking the front-runner Thursday morning.

Here's what to watch Thursday night:

Trump confronts #NeverTrump

Donald Trump is the Republican Party's indisputable front-runner. But rather than rally around him, the GOP is openly revolting, and after months of struggling to fight Trump's candidacy in a coordinated way, there is now a last-ditch movement bubbling up to deny the real estate developer the GOP nomination.

Using the hashtag "#NeverTrump" on social media, Republican strategists, donors, and lawmakers are warning that a Trump nomination would deal a devastating blow to the future of the GOP.

Trump invited a fresh onslaught over the weekend when he repeatedly declined to disavow the Ku Klux Klan and former KKK grand wizard David Duke on CNN's "State of the Union."

GOP Rep. Scott Rigell of Virginia, one of a growing group of congressional Republicans vowing to never back Trump, told CNN's Jake Tapper Wednesday that he would rather, "for the first time in my life," write in a candidate than support Trump.

"He says he admires Putin, he quotes Mussolini. He can't get his way out of a KKK, David Duke reference," Rigell said. "What is missing in the mind of a person who doesn't just immediately reject the KKK and David Duke? He doesn't represent who we are as the Republican Party."

Meanwhile, one anti-Trump super PAC led by former Mitt Romney aide Katie Packer held a conference call with more than 50 top donors and power brokers Tuesday to plot a strategy to prevent Trump from reaching the nomination.

Trump has shown this cycle that he will hit back hard when attacked, and will likely use Thursday's debate to take his critics to task. But he will also want to tread carefully to avoid fueling the anti-Trump campaign. Trump critics believe the next two weeks represent the final window in which they can realistically slow Trump's momentum, and it could actually benefit Trump to lay low, rather than provoke.

Will Trump keep moving to the middle?

After dominating the Super Tuesday contests, Trump chose to forego an election night victory party. Instead, he invited close friends and the media to his property in Palm Beach, Florida, and held a press conference.

It was striking both visually and in tone.

A row of American flags lined the wall behind the podium and a large chandelier hung from the ceiling. With New Jersey Gov. Chris Christie looking on, Trump appeared to be acting out a presidential press conference in the East Room of the White House. As he fielded questions from reporters, there was no mud-throwing at his rivals or lashing out at his critics. And the man who has shocked the country with his divisive rhetoric called for unity.

"I am a unifier — I know people are going to find that a little bit hard to believe, but believe me, I am a unifier," Trump said. "We're going to be more inclusive, I think we're going to be more unified, and I think we're going to be a much bigger party and I think we're going to win in November."

Trump's debate performance Thursday night will show whether this was a temporary or more permanent change in posture for the GOP front-runner, as he looks ahead to the general election. He has already on debate stages defended the non-abortion activities of Planned Parenthood, a distinction from the standard Republican line that could help him in a general election, and called for the U.S. to rebuild its infrastructure on Tuesday night.

Former House Speaker Newt Gingrich said as Trump gets closer to clinching the nomination, it is critical that he start making serious outreach to Republicans across the party, and garner a broad base of support heading into the fall.

"Trump is going to be at a crossroads by March 16. Do I become Reagan or become Goldwater?" Gingrich said. "He has to recognize they have the ability to withhold their support."

Can Cruz and Rubio get hits in against Trump?

Cruz and Rubio can now tout the same message: "I've defeated Donald Trump."

Cruz walked away from Super Tuesday with three additional victories in Texas, Oklahoma and Alaska that add to his victory in Iowa. Rubio, meanwhile, had his first win of the year in Minnesota. As the race moves forward to the March 15 contests, which includes Rubio's home state of Florida, each senator is now urgently positioning themselves to be the candidate that can best take on Trump.

"For the candidates who have not yet won a state, who have not racked up significant delegates, I ask you to prayerfully consider our coming together," Cruz said in his victory speech Tuesday night, in a message that seemed in part aimed at Rubio.

The two men have traded sharp words in recent weeks on issues like immigration, and as they jockey to be the last man standing, expects lots of sparks to fly again.

Cruz and Rubio are also likely to be emboldened by the anti-Trump campaign. Both senators have gone after Trump hard on the campaign trail over the past several weeks, including a memorable CNN debate in Houston last week when they essentially emptied their oppo books.

In his speech to supporters Tuesday night, Cruz hit Trump on a slew of issues including Obamacare, TARP, the "Gang of Eight" immigration bill and Planned Parenthood -- and warned that Trump winning the nomination would be a "disaster for conservatives."

Rubio, who has engaged in a bitterly personal feud with Trump over the last week, also indicated Tuesday night that he will not be letting Trump off the hook.

"Just five days ago, we began to unmask the true nature of the frontrunner so far in this race. We began to explain to the American people that Donald Trump is a con artist," Rubio said in Miami. "And in just five days we have seen the impact that it is having all across the country."

John Kasich isn't going anywhere

John Kasich is starting to stick out like a sore thumb.

With Ben Carson not attending and appearing as if he drop out, the Ohio governor will be the only Republican candidate on the debate stage Thursday night who has not had a single victory in the GOP primary. He finished second to Trump in New Hampshire and Vermont, but that's all.

The calls for Kasich to get out of the 2016 race are quickly intensifying.

As Trump gets closing to clinching the GOP nomination, many Republicans believe that Kasich is making it harder for the party to defeat the GOP front-runner by taking away votes from Rubio.

But even as he's lagging badly in the delegates race, Kasich has shown no signs of abandoning his White House bid before March 15. His home state of Ohio will hold its GOP primary that day, and the governor has vowed to beat Trump there.

On CNN's "New Day" this week, Kasich bristled at the suggestion that his decision to keep running for president is to Rubio's detriment.

"Marco Rubio is trailing in Florida by 17 points. You know what, why aren't they telling him to get out and get behind me?" he said. "I have a better chance of winning in Ohio than he does in Florida. I mean this is nonsense ."

Megyn Kelly versus Donald Trump - again

Trump will confront one of his biggest targets on Thursday -- and it's not a fellow Republican. It's Fox News moderator Megyn Kelly.

Trump has had a rocky on-and-off relationship with the television network throughout his White House campaign, with much of the tension centering around Kelly.

At the first GOP presidential debate of the cycle last summer, Kelly put Trump on the spot for using words like "fat pigs," "dogs," and "disgusting animals" to describe some women. Trump quickly shot back: "Only Rosie O'Donnell."

Since that memorable exchange, Trump has accused Kelly of treating him unfairly. This all came to a head in January, when the GOP front-runner -- angrily hitting back at the network for releasing a mocking statement -- refused to attend a Fox debate in Iowa.

Trump has not threatened to skip this week's Fox debate, setting up a rematch with Kelly.