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 has taken 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.
After criticism of the insult-ridden last debate, Republican leaders wanted a more presidential tone this time.
Mr Trump picked up a key endorsement of Ben Carson hours beforehand.
The retired neurosurgeon dropped out of the race last week and will formally back the New York businessman on Friday.
Who are the Muslims supporting Trump?
Crucial state contests are being held in Florida and Ohio on Tuesday, as Mr Trump's rivals try to make up ground.
Debate highlights so far:
Mr Rubio defends trade deals that mean "America can sell things to people around the world"
Mr Cruz says US brings in too many low-skilled workers which drives down wages of hard working Americans
Sounding like Mr Trump, he says he is going to build a wall, triple the border control and end welfare benefits for undocumented
Mr Trump says he will "make education great" and says former Republican candidate Ben Carson would be involved
Ohio Governor John Kasich says he might be running for president of Croatia if it was not for immigration but the US needs to control the border
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.
On the Democratic side, Vermont Senator Bernie Sanders and former Secretary of State Hillary Clinton are battling for the party's nomination.
Mrs Clinton is leading Mr Sanders in delegate counts so far, though his campaign has proved more formidable than expected.
Both parties will determine their nominees at conventions in July, then Americans will pick their new president in November.