A hasty effort to make peace between Donald Trump and Republican Party leaders veered toward the point of collapse Friday as Jeb Bush announced that he would not back Trump in the general election and Trump unleashed a caustic personal attack on a prominent senator who declined to endorse his campaign.
Since a landslide victory in Indiana made him the presumptive Republican nominee, Trump has faced shunning from party leaders that is unprecedented in modern politics. Trump has struggled to make peace with senior lawmakers and political donors whom he denounced during the Republican primaries, and upon whose largess he must now rely.
In a new sign of the Republican Party's reservations about Trump, the top strategist in charge of defending Republican control of the Senate said in a briefing for lobbyists and donors on Thursday that the party's candidates should feel free to skip the nominating convention in Cleveland in July.
The strategist, Ward Baker, the executive director of the National Republican Senatorial Committee, said that conventions were a distracting spectacle every four years according to two people who attended the briefing, and who spoke on condition of anonymity about the private session. Baker, the attendees said, told Republican lawmakers that they would be better off talking to voters in their home states.
Andrea Bozek, a spokeswoman for the National Republican Senatorial Committee, said that it was up to "each individual campaign" to decide whether to attend the convention.
On Friday, Bush's disavowal of Trump landed as a bitter blow. The former Florida governor is revered among party veterans and has one of the most powerful fundraising networks in Republican politics. In a statement, Bush said his former opponent lacked the "temperament or strength of character" to serve as president.
Bush's father and brother, George Bush and George W. Bush, announced earlier in the week that they would not endorse Trump.
Trump said at a rally in Omaha, Nebraska, that he was untroubled by the Bush family's opposition, and repeated his past mockery of Jeb Bush as a "low-energy person." "I'm not surprised at the Bush family, in all fairness, because I've been very critical of what happened," Trump said.
He reacted with fury to another statement of rejection, from Sen. Lindsey Graham, R-S.C. Graham, a longtime Trump critic who briefly ran for president last year, said Friday that Trump was unfit to be commander in chief.
The populist Manhattan businessman responded with a statement savaging Graham, a senior spokesman for the party on national security. Trump boasted that he "single-handedly destroyed his hapless run for president" and consigned Graham to the political ash heap.
"While I will unify the party, Lindsey Graham has shown himself to be beyond rehabilitation," Trump said. In Omaha, Trump branded Graham "nasty" and called his campaign "a disgrace."
Trump's belittling attack poses a fresh challenge for a party already riven by frustration and indecision over his campaign. Having campaigned for the Republican nomination on a platform of cracking down on immigration and foreign trade, Trump now trails Hillary Clinton in general election polls and cannot afford an exodus of voters, from the Republican base.
While Trump's war on the Republican establishment has galvanized his supporters, it is likely to complicate his efforts to court a broader array of voters, including moderate Republicans, and political benefactors in order to compete in November.
Trump has acknowledged he will need help from the party's traditional bankrollers during the general election, when he has said he will no longer finance his campaign from his personal fortune.
He has appeared uncertain of how to respond to the prospect of mass defections from inside the Republican Party. He has said in recent weeks that he favors party unity as a practical matter, but that there are also Republicans whose support he does not believe he needs — and whose support he would not welcome.
Dan Senor, a former adviser to Mitt Romney and Paul D. Ryan in the 2012 election, said Trump's dismissive attitude toward his critics could have crippling consequences in a general election.
"They're still trying to project this mindset that they're blowing up the place, blowing up the institution," Senor said. "But now they're talking to 120 or 130 million voters, not a few million in a few states."
For a transitory moment on Friday, Trump appeared determined to repair the breach between himself and the party establishment. After clashing sharply with Trump, Ryan, the speaker of the House, announced Friday afternoon that Trump would visit Washington next week, to meet with congressional Republicans and with Ryan privately.
Ryan said Thursday that he was not ready to endorse Trump, a statement widely interpreted as signaling to Republicans that they would face no pressure to close ranks around Trump. In a terse statement, Trump retorted that he did not support Ryan's policy agenda.
Next week's meeting between the two men, Ryan's office said, will concern "Republican principles and ideas that can win the support of the American people this November."
Trump conceded in a television interview Friday morning that he had been surprised by Ryan's rebuke, and he sounded exasperated by the party leadership's unwillingness to rally to his candidacy. "You talk about unity," Trump said, "but what is this?"
Even as he has earned a cold shoulder from much of the party establishment, Trump has also collected important endorsements from deep within the Republican elite. The Senate majority leader, Mitch McConnell, of Kentucky, has committed to supporting him, and Reince Priebus, the Republican National Committee chairman, hastened on Tuesday evening to declare Trump the party's presumptive nominee. Former Vice President Dick Cheney also said in a CNN interview that he would vote for Trump as the Republican nominee.
Sheldon G. Adelson, the billionaire casino owner who is a major benefactor of the party, said Thursday at an event in Manhattan that he would support Trump. Gov. Pete Ricketts of Nebraska, whose family financed millions of dollars' worth of ads attacking Trump in the primaries, introduced Trump in Omaha on Friday.
Most Republican campaign contributors face less immediate pressure to count themselves as with or against Trump, but strategists expect Trump to face considerable skepticism. John McKager Stipanovich, a longtime Florida lobbyist and fundraiser close to Jeb Bush, said Trump would face stiff resistance among the people on which the party has typically relied for financial support.
Stipanovich predicted that the stances taken by Ryan and the Bush family would hurt Trump with traditional party donors.
"Obviously, Trump has spent an awful lot of time in the last year disparaging people like that," said Stipanovich, who has vowed to oppose Trump. "It will be some indication of how craven they are to see how quickly they crawl to him on their knees, or to the party to help him. I don't know that they will do that."