WASHINGTON • Billionaire Donald Trump's unabashed and continuing hostility towards the parents of a slain Muslim American soldier, and his attacks on Republican leaders who have rebuked him for it, has threatened to shatter his uneasy alliance with the Republican Party at the outset of the election campaign.

Ignoring the pleas of his advisers and entreaties from party leaders in Washington, the Republican presidential nominee only dug in further on Tuesday, telling a Virginia television station that he had no regrets about his clash with Mr Khizr Khan and his wife Ghazala.

And in an extraordinarily provocative interview with The Washington Post, Mr Trump declined to endorse for re-election several Republicans who had criticised him, including House Speaker Paul Ryan of Wisconsin and Senator John McCain of Arizona, who both face primaries this month. He also belittled Senator Kelly Ayotte of New Hampshire for not being supportive of his campaign.

For days, Mr Trump's top advisers and allies have urged him to move on from the feud and focus instead on the economy and the national security record of his Democratic opponent Hillary Clinton.

Mrs Clinton has already picked up a few telling Republican endorsements: Ms Meg Whitman, the Hewlett-Packard executive who ran for governor of California as a Republican, backed her on Tuesday, as did Representative Richard Hanna of New York, a moderate Republican. Both denounced Mr Trump's treatment of the Khan family.

Yet, facing outcry on the left and right, the Trump campaign has left open the door to continued conflict with the family. A memo circulated by Mr Trump's aides on Tuesday to his campaign surrogates urged them to express gratitude for the Khans' sacrifice, but added that Mr Trump had a "right to defend himself", according to a person who received the document.

Republicans now say his obstinacy in addressing the crisis may trigger drastic defections within the party, and Republican lawmakers and strategists have begun to entertain abandoning him en masse. However, the Republican Party has not yet come close to abandoning his candidacy.

Amid the war of words with the military family, Mr Trump stoked controversy further on Tuesday at a rally in Virginia when he told supporters that a veteran had given him a Purple Heart medal earlier in the day. The military honour is given to a member of the armed forces who is killed or wounded in combat.

"I always wanted to get the Purple Heart," he said. "This was much easier."

He has never served in the military and, on Monday, The New York Times reported that he had received five draft deferments during the Vietnam War, several for his studies and one for bone spurs in his feet, which meant he was not called up to serve.

His statement immediately started trending on Twitter, with some users mocking the real estate mogul for accepting the honour while on the campaign trail.

Mrs Clinton also jumped on his remarks. "This from a man who says he's 'sacrificed' for our country," she posted on Twitter minutes after.

NEW YORK TIMES, AGENCE FRANCE-PRESSE