Presidential hopeful Marco Rubio has his last chance to make an impact in a Republican debate before Tuesday’s do-or-die contest in Florida.
He will take to the stage in his home city of Miami a long way behind Donald Trump and Ted Cruz in the race to be his party’s nominee.
Mr Trump said he expects the debate to be “softer” this time, after personal insults characterised the last one.
He picked up a key endorsement of Ben Carson hours before the debate.
The retired neurosurgeon dropped out of the race last week and will formally back the New York businessman on Friday, according to the Washington Post and ABC News.
After widespread criticism of the last debate, Republican leaders want a more presidential tone this time around.
Republican National Committee Chairman Reince Priebus told CNN he had taken steps to ensure this debate would be “more of a G-rated debate” than others.
Obama: ‘Don’t blame me for Trump’
Who are the Muslims supporting Trump?
Crucial state contests are being held in Florida and Ohio next week, as Mr Trump’s rivals try to make up ground.
Ohio Governor John Kasich and Florida Senator Mr Rubio are under pressure to win their home states.
There are 350 delegates up for grabs on Tuesday, with the winner taking all in Florida.
Mr Trump, a billionaire businessman from New York with no political experience in office, has dominated the news, the polls and the state primary contests so far.
On Wednesday, he added to his list of controversial remarks when he told CNN: “I think Islam hates us, there’s a tremendous hatred. We have to get to the bottom of it.”
There were signs that Mr Trump has been more conciliatory of late.
After additional state wins on Tuesday night, he said he had “great respect” for House Speaker Paul Ryan.
He also discouraged booing at the mention of former Republican presidential candidate Mitt Romney’s name and urged the Republican party to “unify” behind him.
The next votes
15 March: Florida, Illinois, Missouri, North Carolina, Ohio Primaries
22 March: Arizona Primary, Utah Caucuses, Idaho Caucuses (Democratic)
26 March: Alaska, Hawaii, Washington Caucuses (Democratic)
1 April: North Dakota Caucuses (Republican)
5 April: Wisconsin Primary
9 April: Wyoming Caucuses (Democratic)
19 April: New York Primary