The scenario Karl Rove outlined was bleak.
Addressing a luncheon of Republican governors and donors in Washington on Feb. 19, he warned that Donald J. Trump’s increasingly likely nomination would be catastrophic, dooming the party in November. But Mr. Rove, the master strategist of George W. Bush’s campaigns, insisted it was not too late for them to stop Mr. Trump, according to three people present.
At a meeting of Republican governors the next morning, Paul R. LePage of Maine called for action. Seated at a long boardroom table at the Willard Hotel, he erupted in frustration over the state of the 2016 race, saying Mr. Trump’s nomination would deeply wound the Republican Party. Mr. LePage urged the governors to draft an open letter “to the people,” disavowing Mr. Trump and his divisive brand of politics.
The suggestion was not taken up. Since then, Mr. Trump has only gotten stronger, winning two more state contests and collecting the endorsement of Gov. Chris Christie of New Jersey.
In public, there were calls for the party to unite behind a single candidate. In dozens of interviews, elected officials, political strategists and donors described a frantic, last-ditch campaign to block Mr. Trump — and the agonizing reasons that many of them have become convinced it will fail. Behind the scenes, a desperate mission to save the party sputtered and stalled at every turn.
Efforts to unite warring candidates behind one failed spectacularly: An overture from Senator Marco Rubio to Mr. Christie angered and insulted the governor. An unsubtle appeal from Mitt Romney to John Kasich, about the party’s need to consolidate behind one rival to Mr. Trump, fell on deaf ears.
At least two campaigns have drafted plans to overtake Mr. Trump in a brokered convention, and the Senate majority leader, Mitch McConnell of Kentucky, has laid out a plan that would have lawmakers break with Mr. Trump explicitly in a general election.
Despite all the forces arrayed against Mr. Trump, the interviews show, the party has been gripped by a nearly incapacitating leadership vacuum and a paralytic sense of indecision and despair, as he has won smashing victories in South Carolina and Nevada. Donors have dreaded the consequences of clashing with Mr. Trump directly. Elected officials have balked at attacking him out of concern that they might unintentionally fuel his populist revolt. And Republicans have lacked someone from outside the presidential race who could help set the terms of debate from afar.
The endorsement by Mr. Christie, a not unblemished but still highly regarded figure within the party’s elite — he is a former chairman of the Republican Governors Association — landed Friday with crippling force. It was by far the most important defection to Mr. Trump’s insurgency: Mr. Christie may give cover to other Republicans tempted to join Mr. Trump rather than trying to beat him. Not just the Stop Trump forces seemed in peril, but also the traditional party establishment itself.
Should Mr. Trump clinch the presidential nomination, it would represent a rout of historic proportions for the institutional Republican Party, and could set off an internal rift unseen in either party for a half-century, since white Southerners abandoned the Democratic Party en masse during the civil rights movement.
Former Gov. Michael O. Leavitt of Utah, a top adviser to Mr. Romney’s 2012 presidential campaign, said the party was unable to come up with a united front to quash Mr. Trump’s campaign.
“There is no mechanism,” Mr. Leavitt said. “There is no smoke-filled room. If there is, I’ve never seen it, nor do I know anyone who has. This is going to play out in the way that it will.”
Resistance Runs Deep
Republicans have ruefully acknowledged that they came to this dire pass in no small part because of their own passivity. There were ample opportunities to battle Mr. Trump earlier; more than one plan was drawn up only to be rejected. Rivals who attacked him early, like Rick Perry and Bobby Jindal, the former governors of Texas and Louisiana, received little backup and quickly faded.
Late last fall, the strategists Alex Castellanos and Gail Gitcho, both presidential campaign veterans, reached out to dozens of the party’s leading donors, including the casino magnate Sheldon Adelson and the hedge-fund manager Paul Singer, with a plan to create a “super PAC” that would take down Mr. Trump. In a confidential memo, the strategists laid out the mission of a group they called “ProtectUS.”
“We want voters to imagine Donald Trump in the Big Chair in the Oval Office, with responsibilities for worldwide confrontation at his fingertips,” they wrote in the previously unreported memo. Mr. Castellanos even produced ads portraying Mr. Trump as unfit for the presidency, according to people who saw them and who, along with many of those interviewed, insisted on anonymity to discuss private conversations.
The two strategists, who declined to comment, proposed to attack Mr. Trump in New Hampshire over his business failures and past liberal positions, and emphasized the extreme urgency of their project. A Trump nomination would not only cause Republicans to lose the presidency, they wrote, “but we also lose the Senate, competitive gubernatorial elections and moderate House Republicans.”
No major donors committed to the project, and it was abandoned. No other sustained Stop Trump effort sprang up in its place.
Resistance to Mr. Trump still runs deep. The party’s biggest benefactors remain totally opposed to him. At a recent presentation hosted by the billionaires Charles G. and David H. Koch, the country’s most prolific conservative donors, their political advisers characterized Mr. Trump’s record as utterly unacceptable, and highlighted his support for government-funded business subsidies and government-backed health care, according to people who attended.
But the Kochs, like Mr. Adelson, have shown no appetite to intervene directly in the primary with decisive force.
The American Future Fund, a conservative group that does not disclose its donors, announced plans on Friday to run ads blasting Mr. Trump for his role in an educational company that is alleged to have defrauded students. But there is only limited time for the commercials to sink in before some of the country’s biggest states award their delegates in early March.
Instead, Mr. Trump’s challengers are staking their hopes on a set of guerrilla tactics and long-shot possibilities, racing to line up mainstream voters and interest groups against his increasingly formidable campaign. Donors and elected leaders have begun to rouse themselves for the fight, but perhaps too late.
Two of Mr. Trump’s opponents have openly acknowledged that they may have to wrest the Republican nomination from him in a deadlocked convention.
Speaking to political donors in Manhattan on Wednesday evening, Mr. Rubio’s campaign manager, Terry Sullivan, noted that most delegates are bound to a candidate only on the first ballot. Many of them, moreover, are likely to be party regulars who may not support Mr. Trump over multiple rounds of balloting, he added, according to a person present for Mr. Sullivan’s presentation, which was first reported by CNN.
Advisers to Mr. Kasich, the Ohio governor, have told potential supporters that his strategy boils down to a convention battle. Judd Gregg, a former New Hampshire senator who had endorsed Jeb Bush, said Mr. Kasich’s emissaries had sketched an outcome in which Mr. Kasich “probably ends up with the second-highest delegate count going into the convention” and digs in there to compete with Mr. Trump.
Several senior Republicans, including Mr. Romney, have made direct appeals to Mr. Kasich to gauge his willingness to stand down and allow the party to unify behind another candidate. But Mr. Kasich has told at least one person that his plan is to win the Ohio primary on March 15 and gather the party behind his campaign if Mr. Rubio loses in Florida, his home state, on the same day.
In Washington, Mr. Kasich’s persistence in the race has become a source of frustration. At Senate luncheons on Wednesday and Thursday, Republican lawmakers vented about Mr. Kasich’s intransigence, calling it selfishness.
One senior Republican senator, noting that Mr. Kasich has truly contested only one of the first four states, complained: “He’s just flailing his arms around and having a wonderful time going around the country, and it just drives me up the wall.”
Mr. McConnell was especially vocal, describing Mr. Kasich’s persistence as irrational because he has no plausible path to the nomination, several senators said.
While still hopeful that Mr. Rubio might prevail, Mr. McConnell has begun preparing senators for the prospect of a Trump nomination, assuring them that, if it threatened to harm them in the general election, they could run negative ads about Mr. Trump to create space between him and Republican senators seeking re-election. Mr. McConnell has raised the possibility of treating Mr. Trump’s loss as a given and describing a Republican Senate to voters as a necessary check on a President Hillary Clinton, according to senators at the lunches.
He has reminded colleagues of his own 1996 re-election campaign, when he won comfortably amid President Bill Clinton’s easy re-election. Of Mr. Trump, Mr. McConnell has said, “We’ll drop him like a hot rock,” according to his colleagues.
The Rubio Hope
There is still hope that Mr. Rubio might be able to unite much of the party and slow Mr. Trump’s advance in a series of big-state primaries in March, and a host of top elected officials endorsed him over the last week. But Mr. Rubio has struggled to sideline Mr. Kasich and Senator Ted Cruz of Texas, who is running a dogged campaign on the right. He has also been unable to win over several of his former rivals who might help consolidate the Republican establishment more squarely behind him.
Mr. Rubio showed a lack of finesse in dealing with his fallen rivals’ injured egos.
Mr. Christie had attacked Mr. Rubio contemptuously in New Hampshire, calling him shallow and scripted, and humiliating him in a debate. Nevertheless, Mr. Rubio made a tentative overture to Mr. Christie after his withdrawal from the presidential race. He left the governor a voice mail message, seeking Mr. Christie’s support and assuring him that he had a bright future in public service, according to people who have heard Mr. Christie’s characterization of the message.
Mr. Christie, 53, took the message as deeply disrespectful and patronizing, questioning why “a 44-year-old” was telling him about his future, said people who described his reaction on the condition of anonymity. Further efforts to connect the two never yielded a direct conversation.
Mr. Trump, by contrast, made frequent calls to Mr. Christie once he dropped out, a person close to the governor said. After the two met at Trump Tower on Thursday with their wives, Mr. Christie flew to Texas and emerged on Friday to back Mr. Trump and mock Mr. Rubio as a desperate candidate near the end of a losing campaign.
‘Verging on Panic’
Efforts to reconcile Mr. Rubio and Mr. Bush, a former governor of Florida, have been scarcely more successful, dating to before the South Carolina primary, when Mr. Rove reached out to their aides to broker a cease-fire, according to Republicans familiar briefed on the conversations. It did not last.
Mr. Bush has been nearly silent since quitting the race Feb. 20, playing golf with his son Jeb Jr. in Miami and turning to the task of thank-you notes. In a Wednesday conference call with supporters, he did not express a preference among the remaining contenders. When Mr. Rubio called him on Monday, their conversation did not last long, two people briefed on it said, and Mr. Rubio did not ask for his endorsement.
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“There’s this desire, verging on panic, to consolidate the field,” said Senator Lindsey Graham of South Carolina, a former supporter of Mr. Bush. “But I don’t see any movement at all.”
Mr. Rubio’s advisers were also thwarted in their efforts to secure an endorsement from Mr. Romney, whom they lobbied strenuously after the Feb. 20 South Carolina primary.
Mr. Romney had been eager to tilt the race, and even called Mr. Christie after he ended his campaign to vent about Mr. Trump and say he must be stopped. On the night of the primary, Mr. Romney was close to endorsing Mr. Rubio himself, people familiar with his deliberations said.
Yet Mr. Romney pulled back, instead telling advisers that he would take on Mr. Trump directly.
After a Tuesday night dinner with former campaign aides, during which he expressed a sense of horror at the Republican race, Mr. Romney made a blunt demand Wednesday on Fox News: Mr. Trump must release his tax returns to prove he was not concealing a “bombshell” political vulnerability.
Mr. Trump responded only with casual derision, dismissing Mr. Romney on Twitter as “one of the dumbest and worst candidates in the history of Republican politics.”
Mr. Romney is expected to withhold his support before the voting this week on the so-called Super Tuesday, but some of his allies have urged him to endorse Mr. Rubio before Michigan and Idaho vote March 8. Mr. Romney grew up in Michigan, and many Idahoans are fellow Mormons.
But already, a handful of senior party leaders have struck a conciliatory tone toward Mr. Trump. Representative Kevin McCarthy of California, the House majority leader, said on television that he believed he could work with him as president. Many in the party acknowledged a growing mood of resignation.
Fred Malek, the finance chairman of the Republican Governors Association, said the party’s mainstream had simply run up against the limits of its influence.
“There’s no single leader and no single institution that can bring a diverse group called the Republican Party together, behind a single candidate,” Mr. Malek said. “It just doesn’t exist.”
On Friday, a few hours after Mr. Christie endorsed him, Mr. Trump collected support from a second governor, who in a radio interview said Mr. Trump could be “one of the greatest presidents.”
That governor was Paul LePage.