Miami, US: Republican White House hopefuls gathered for a heavyweight debate on Thursday in Florida, a crown jewel in the nominations race where frontrunner Donald Trump aims to deliver a knockout blow against Marco Rubio on the senator’s home turf.

Floridians vote on 15 March, along with residents of Ohio and Illinois. All three big states are winner-take-all in the Republican delegate race, the first such contests in the 2016 cycle.

Many in the party see next Tuesday’s votes as the last best chance to derail the billionaire real estate moguls’ insurgent candidacy. Florida will most likely give one candidate huge momentum, and potentially spell doom for its native son.

Just as Trump sought to appear more presidential and unify the party, looking beyond the contentious primaries to a possible general election showdown with Democratic frontrunner Hillary Clinton, he unleashed a stunning new provocation.

‘I think Islam hates us,’ Trump told CNN in an interview aired Wednesday night in the latest example of his controversial bluster. ‘There’s something there, a tremendous hatred there. We have to get to the bottom of it.’

Trump caused a global firestorm in December when he called for a ban on Muslims entering the United States.

Four men will take the stage in Miami: Trump, Rubio, Senator Ted Cruz of Texas, and Ohio Governor John Kasich.

Trump is by all accounts the man to beat. He emerged strengthened by victories Tuesday in Michigan, Mississippi and Hawaii, and has now won 15 of 24 races.

And he has boldly predicted he will win Rubio’s Florida and Kasich’s Ohio, which would essentially be the final nail in the coffin for their campaigns.

‘If I win those two I think it’s over,’ Trump told CNN Wednesday.

Rubio was championed by party luminaries as the best mainstream hope of derailing Trump, but he has performed dreadfully in several recent primary contests, including those Tuesday.

Trump leads Rubio in Florida by a dramatic 43 percent to 20 percent among likely Republican primary voters, according to a Fox News poll released Wednesday, while Kasich leads in his own state with 34 percent support.

Florida Governor Rick Scott, a Republican, insisted his state had ‘the most important primary’ of the cycle and whoever wins it will be a major advantage.

‘It’s the biggest swing state, it will decide the presidency in the fall,’ Scott told reporters at the debate site.

Rubio on the ropes

With his campaign on the verge of fizzling, Rubio stressed it was crucial to gang up on the frontrunner.

But in his home state, Rubio called on all Republicans to get behind him as part of his anti-Trump rallying cry, including those supporting Kasich or Cruz.

‘If you are truly committed to denying Donald Trump 99 delegates in the state of Florida, then people that are voting for John Kasich or Ted Cruz, at least in Florida, need to vote for Marco Rubio,’ he said.

‘I’m the only one that has a chance to beat him here.’

Cruz, who has emerged as the most viable anti-Trump candidate, is aiming to spoil any Rubio resurgence, campaigning heavily here in the run up to the primary.

And in a move that proved a very long time coming, Cruz finally received the first endorsement from a fellow senator, Mike Lee of Utah.

‘We’ve reached a point when we need to unite behind a single candidate,’ Lee told reporters as he highlighted Cruz’s commitment to conservative principles and uncompromising style in Congress—one that has earned the wrath of several colleagues.

‘Ted doesn’t believe you should settle,’ he added. ‘Don’t settle.’

Piling on, former candidate and retired neurosurgeon Ben Carson told Fox radio that he was ‘certainly leaning’ toward endorsing Trump. US media including CBS News reported Carson’s endorsement would come on Friday.

President Barack Obama meanwhile waded into the contest over who will be his successor, and while he expressed regret that the ‘nasty tone of our politics has accelerated rather than waned’ since he moved into the White House, he rejected suggestions he was to blame for the rise of Trump.

‘What I’m not going to do is to validate some notion that the Republican crackup that’s been taking place is a consequence of actions that I’ve taken,’ Obama said.