Instead of ousting Mr. Trump and forcing him to run as a third-party candidate, Republican elites now find themselves, or their preferred candidates, losing control of their own party. After the meeting of anti-Trump conservatives last Thursday, one of the meeting’s organizers, the right-wing radio host Erick Erickson, put out a statement from the group.

“We intend to keep our options open as to other avenues to oppose Donald Trump,” he wrote. “Our multiple decades of work in the conservative movement for free markets, limited government, national defense, religious liberty, life and marriage are about ideas, not necessarily parties.”

It is noteworthy that Mr. Trump is running a campaign safely within the two-party system, considering he is a Voltron-like candidate built using the most successful parts of past independent campaigns.

Like George Wallace, the former Alabama governor who ran a third-party presidential campaign in 1968 after his segregationist views put him on the fringes of the Democratic Party, Mr. Trump uses strident racial language to stoke his supporters’ anger. Like Ross Perot, who won 19 percent of the popular vote as an independent in 1992, Mr. Trump is an eccentric billionaire who is fun to watch on TV, which has allowed him to move ahead without relying on traditional fund-raising channels. Like Pat Buchanan, the Reform Party candidate in 2000, he is repackaging warmed-over economic and cultural nationalism and selling it as the future of the conservative movement. Mr. Trump even has a bit of Teddy Roosevelt, whose penchant for strongman bluster made him a populist hero when he ran as the Progressive (a.k.a. Bull Moose) Party candidate in 1912.

For now, the Republican Party’s leaders are trying to maintain some semblance of control over what’s happening to them. Appearing on ABC’s “This Week” on Sunday, Reince Priebus, the chairman of the Republican National Committee, said it was both too early and too late for his party to think about starting an independent bid.

The host, George Stephanopoulos, asked Mr. Priebus what he thought of the Stop Trump movement, and whether recruiting a third-party candidate would doom the Republican chances of winning back the White House. “Well, sure it would — of course it would,” he said. “But it isn’t likely, and it’s probably too late, and there is no definitive answer right now as to who the nominee is going to be of our party. So I think all of it’s far too early.”

It’s Schrödinger’s primary now: both alive and dead, too early to speculate about and too late to save. Worst of all, the anti-Trump movement’s only hope to save the party might be a Libertarian. According to Julia Azari, a professor of political science at Marquette University, a Trump victory would actually prove worse for the Republican Party in the long run than another Democratic presidency.