Billionaire looking for a running mate after Kasich pulls out of the Republican race.

Donald Trump has assumed control of the Republican Party as its presumptive presidential nominee and now faces the arduous task of coalescing a party deeply divided over his toxic brand of politics.

Trump moved swiftly to consider vice-presidential prospects and plan for what is likely to be a costly and vicious six-month battle for the White House against Democrat Hillary Clinton after Ohio Governor John Kasich exited the Republican race.

Trump, who has proudly touted how he has self-funded his campaign, said he would begin actively seeking donations for his campaign and raise money for the national party.

Party leaders are now though scrambling to stave off a parade of prominent Republicans endorsing Clinton, but already there were notable defections.


The two living Republican past presidents, George H.W. Bush and George W. Bush, have no plans to endorse Trump, according to their spokesmen.

In the swing state of Nevada, Governor Brian Sandoval, a moderate Republican and rising Latino star, said he plans to vote for Trump despite their disagreements on some issues. But Republican Nevada Senator Dean Heller said "I vehemently oppose our nominee" because he disparaged women, Hispanics and veterans - although Heller insisted he would not vote for Clinton.

Democrats rushed to exploit the moment. The Clinton campaign released a brutal video mash-up of Republican rivals condemning his character and fitness for office, while the former Secretary of State called him "a loose cannon" and invited Republicans and independents seeking an alternative to Trump to join her.

"Let's get off the red or the blue team. Let's get on the American team," Clinton said on CNN.

In states coast to coast, meanwhile, Democrats tried to link embattled Republican senators and other officeholders to Trump in hopes that the shrapnel from his polarising candidacy would impair Republicans down the ballot.

Some Republicans tried to keep mum about Trump, and others gave puzzling statements that sought to walk a tightrope between embracing him and distancing themselves from him.

As some conservative commentators lit up social media with images of burning GOP registration cards, some party elders called for a healing process and sought to quiet talk of an independent protest candidacy.

"Life is a series of choices, and this choice looks like one between Donald Trump and Hillary Clinton," said Haley Barbour, a former Mississippi governor and national party chairman.

"Anybody who proposes a third party is saying, 'Let's make sure Clinton wins'."

George W. Bush and his father reportedly have no plans to endorse Donald Trump. Photo / AP
George W. Bush and his father reportedly have no plans to endorse Donald Trump. Photo / AP

Senate Majority Leader Mitch McConnell stood with Trump: "As the presumptive nominee, he now has the opportunity and the obligation to unite our party around our goals."

Trump said he was hardly fretting about whether leading Republicans, such as 2012 presidential nominee Mitt Romney, would eventually back him.

"I believe that the people are going to vote for the person," Trump said in an interview. "They love their party, but until this year the party was going in the wrong direction ... We've made the party much bigger."

Trump spent yesterday holed up in his soaring New York skyscraper, plotting ways to repair his image and destroy the opponent he calls "Crooked Hillary".

He said he was shellshocked by his sudden emergence as the Republican standard-bearer, having anticipated that his fight with Texas Senator Ted Cruz and Kasich would continue until June's California nominating contest. Kasich left the race yesterday, a day after Cruz, in the wake of Trump's resounding primary win in Indiana on Wednesday.

Trump and his advisers yesterday began making decisions about the general election. Though he has repeatedly touted his ability to self-finance his campaign, Trump said that he would seek donations going forward, especially small-dollar contributions from grassroots supporters.

So far, Trump has given or loaned his campaign more than US$36 million ($52.1 million) and accepted an additional US$12 million in donations.

As presumptive nominee, Trump will help shape the programming of the party's July convention in Cleveland, and the convention and Trump staffs will begin working together.

The Trump campaign will quickly expand beyond what has been a relatively skeletal staff to do battle with Clinton's sprawling operation. Trump told the Washington Post that he was weighing potential running mates and that he wanted someone with governing experience and with whom he has a good rapport, citing Barack Obama's selection of Joe Biden as a model.

"In all fairness, when Obama chose Biden, it was an odd choice, and yet they have very good chemistry together and therefore it was a good choice for them," Trump said. "So having good chemistry is very important."

Trump said he has his eyes on Kasich, saying that during intermissions at debates the two gravitated toward each other. "I've always liked him and I've always gotten along with him," Trump said.

Is he on the short list? "Let's put it this way," Trump said, "he's rising rapidly."

Trump said he was eager to start receiving regular classified intelligence briefings from the US Government - a tradition for party nominees - and said he hoped to work with GOP congressional leaders to co-ordinate a cohesive policy agenda for the fall campaign.

"I'm very much a team player, and I look forward to working with Mitch McConnell and Paul Ryan and Kevin McCarthy and everybody," he said.

But Trump dismissed the idea of toning down his rhetoric and vowed to stand by his earlier, controversial calls to temporarily ban Muslims from entering the US and to deport millions of undocumented immigrants.

"I really feel that it's important that I do what's right as opposed to necessarily cater to what's going to play to the voters," Trump said. "Because nobody really knows what plays with the voters, and I'm an example of that. If I tested some of the things I say out in polling, I probably wouldn't do very well."