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 toJohn 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.