Donald Trump’s last remaining challenger for the Republican Party presidential nomination, John Kasich, has dropped out of the race, leaving the presumptive nominee with the task of uniting a fractured party around his White House bid.

“As I suspend my campaign today, I have renewed faith — deeper faith — that the Lord will show me the way forward,” Ohio Governor Kasich told supporters, ending his effort to block Mr Trump from becoming the party’s 2016 standard-bearer.

Mr Kasich, who had stubbornly persisted with his campaign despite never having a viable path to the nomination, cancelled a planned media appearance on Wednesday in Virginia to announce his withdrawal from Ohio instead.

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Mr Kasich’s departure will clear the field for Mr Trump after the real estate mogul’s chief rival, US Senator Ted Cruz, ended his campaign on Tuesday following his defeat in Indiana’s Republican primary contest.

But Mr Trump faces persistent opposition from some party loyalists who fear his positions on key issues could set up Republicans for massive losses to the Democrats in the November 8 election.

Trump spokeswoman Katrina Pierson said on MSNBC that Mr Trump believes more Republicans will support him when they consider the possibility of Hillary Clinton, favourite to be the Democratic nominee, being elected president.

“They’re going to come around,” she said.

Mrs Clinton warned the United States should not take a risk on an unreliable candidate like Mr Trump.

“He is a loose cannon and loose cannons tend to misfire,” she said in an interview with CNN, citing what she said was Mr Trump’s claim that climate change was a Chinese hoax.

Mrs Clinton said Mr Trump would have to offer policy specifics in the lead up to the election and that she knows how to run against him.