Trump nomination divides Republicans

Top Republicans are divided on whether to support Donald Trump after the businessman all but secured the party's presidential nomination.

Some took to social media to disavow their membership in the party by burning their voter registration forms.

Others though started to fall in line behind the candidate, saying Trump is vastly preferable to Hillary Clinton, the likely Democratic nominee.

Trump is deeply unpopular among many key voting blocs in the US.

"If we nominate Trump, we will get destroyed... and we will deserve it," South Carolina Senator Lindsay Graham said on Tuesday after Texas Senator Ted Cruz dropped out of the race, effectively clearing a path for Trump.

Others such as former Louisiana Governor Bobby Jindal, who have been harsh critics of Trump in the past, said they would support him in the general election.

"There's a lot about Donald Trump that I don't like, but I'll vote for Trump over Hillary any day," said Ari Fleischer, press secretary for former President George W Bush

Considered a long shot when he launched his campaign in June, Trump has decisively won a large number of states across the US, defeating an experienced field of rivals.

Ohio Governor John Kasich has vowed to remain in the Republican race, but trails far behind Trump in terms of delegates.

Some Republican analysts fear Trump's candidacy could have a crippling effect on down-ballot races, giving Democrats the chance to retake the Senate and possibly, but less likely, the House.

Republican senators up for re-election in Democratic leaning states such as Kelly Ayotte in New Hampshire and Pat Toomey in Pennsylvania have sought to distance themselves from Trump.

There are concerns about some of his policies on immigration and national security, like building a wall on the southern US border paid for by Mexico, a ban on Muslims coming to the US and the killing of the families of terrorists.

Some Republicans are considering drafting a third party candidate to challenge Trump. Photo: AP

Although Cruz left the race on Tuesday, he did not throw his support behind Trump.

Personal attacks between the two candidates grew intense in recent weeks.

Trump ridiculed Cruz's wife, Heidi, and suggested that Cruz's father was connected to Lee Harvey Oswald, the man who killed President John F Kennedy.

On Tuesday, Cruz attacked the billionaire businessman as a "pathological liar" and "serial philanderer".

The unease among top Republicans is likely to complicate Trump's search for a running mate.

Trump has said he wants a vice-presidential nominee with political experience to balance the ticket.

A senior adviser for Jeb Bush merely laughed when the New York Times asked whether the former Florida Governor would consider being Trump's running mate.

Ed Goeas, an adviser to Scott Walker also ruled out the Wisconsin governor.

"Scott Walker has a visceral negative reaction to Trump's character," Goeas told the Times.