NEW YORK - Former US Presidents George HW Bush and George W Bush, the two living Republican heads of state, will not endorse Donald Trump, their spokesmen have announced.

The announcement comes as Trump, the likely Republican presidential nominee, seeks to overcome deep dissent within the party’s ranks ahead of a likely face-off against Hillary Clinton, the Democratic front-runner, in the November general elections.

In a break with traditional election year party solidarity, neither George Bush senior or George W Bush plan to endorse Trump, whose a resounding win in the Indiana primary led his opponents Senator Ted Cruz and Ohio Governor John Kasich to drop out of the race pacing the way for the billionaire businessman to becomes the Republicans’ nominee the clinch the to job.

The former presidents’ detached stance highlights Trump’s challenge as he seeks to consolidate his support.

The 91-year-old George Bush senior has endorsed every Republican nominee for the past five decades but a spokesman said he was “retired from politics”, the Washington Post reported.

Meanwhile, a personal aide of his son, George W Bush, said the 43rd president “does not plan to participate in or comment on the presidential campaign”. Like his father, George W Bush endorsed the last two Republican nominees for president — Senator John McCain in 2008 and former Governor Mitt Romney in 2012.

During the primary contest, Trump repeatedly lambasted George W Bush’s brother Jeb, the former Florida governor, whom he derided as “low energy” and whom he forced from the presidential race after a commanding victory in the South Carolina primary in February.

Some Republican commentators said Trump had a broader problem in winning support from the party’s old order.

“Some establishment Republicans will break for Trump, but the party will be very sharply divided,” Tony Fratto, a former top official in the George W Bush administration, said. “Traditional (Republican) financial contributors are staying out of the race. Large numbers of Republicans will either stay home or actually vote for Hillary Clinton. Traditional Republicans are simply disgusted by Trump and will never support him.”

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In the wake of his Indiana victory, Trump himself fired a shot across the bows of the party establishment after recent comments from several high-profile Republicans that they could never support him.

“Honestly, there are some people I really don’t want. I don’t think it is necessary. People will be voting for me; they’re not voting for the party,” he told NBC.

But speaking after Ted Cruz, the senator, quit the race, Trump said he was “confident that I can unite much” of the Republican party. His coronation as Republican flag-bearer appeared complete when John Kasich, the Ohio governor, suspended his campaign on Wednesday, the last Trump challenger to fall by the wayside.

Trump heads towards November’s election following a primary campaign in which a deep anti-establishment mood helped him emerge as the unlikely victor from a record field of 17 contenders.

But analysts are split as to whether the former host of The Apprentice, who has spent as much time lambasting his party as he has hitting at Mrs Clinton, can now rally a Republican establishment that has long believed that he was anathema to its values.

“The party definitely needs to rally behind him if they want to win the election,” David Gergen, a politics expert at Harvard’s Kennedy School of Government, said. “There is a possibility that he will win but that depends on getting the vast majority of Republicans behind him and then expanding beyond into the independent pool [of voters].”

A new CNN/ORC poll gave Mrs Clinton a 13-point lead over Trump in the general election race, while an average of recent polls compiled by Real Clear Politics gives her a narrower lead of 6.5 per cent. But some experts, including Democrats who remember how the party underestimated Ronald Reagan in 1980, point out that Mr Trump has shown a remarkable ability to upend conventional political wisdom at every juncture.

Reince Priebus, the Republican National Committee chairman who has sparred with Trump, said it was time to patch up differences. “We’ve got to unify, we need time to unify. And we will unify. ”

But several high-profile Republicans, including Romney, have said they could never support the tycoon. Before the Indiana results emerged, Lindsey Graham, the South Carolina senator, tweeted that “If we nominate Trump, we will get destroyed?…?and we will deserve it”.

Bobby Jindal, the former Louisiana governor, said on Tuesday he would vote for Trump over Mrs Clinton but was “not happy” about the prospect. Some senior Republicans have said privately that they would vote for Mrs Clinton over Trump because of her strength on national security.

Meanwhile, in an interview with CNN, Trump weighed in on pressing foreign policy issues, including how his proposal to ban Muslims would impact US relations with Muslim nations and the moves Russian warplanes have made recently near US naval ships.

Trump did not back away from his position to ban all foreign Muslims from entering the US, but said he would work with Muslim countries in the fight against terrorism.

“They (Muslim countries) have to save themselves, and we can help them, but they have to save themselves,” Trump said.

On Russian moves, Trump said he would be able to call Russian President Vladimir Putin and get him to keep his warplanes far from American military ships by simply saying: “Don’t do it again.”

“I think I will have a good relationship with him,” Trump said of Putin, the Russian president, who in December called Trump “talented” and “absolutely the leader in the presidential race.”