A few weeks ago, Mike Pence did what no other vice president in the modern era has done: He refused to endorse the re-election of the president under whom he served. When it comes to alumni of Donald Trump’s administration, Mr. Pence is hardly alone; the list of high-ranking officials who worked for Mr. Trump and have implied or outright stated that they can’t support their former boss under any circumstances has grown to an astonishing length.

The list of prominent Republican figures who did not serve Mr. Trump and regard him as unacceptable is equally impressive. It includes the 2012 Republican nominee for president, Mitt Romney, and his running mate, the former speaker of the House Paul Ryan, as well as Liz Cheney, who served in the House Republican leadership, and her father, the former vice president Dick Cheney, who summarized the situation bluntly: “There has never been an individual who is a greater threat to our republic than Donald Trump.”

Despite Mr. Trump’s almost effortless sweep of the Republican nomination contest, there remain deep pockets of resistance to him in the ranks. More than a fifth of voters in the Republican primaries supported Nikki Haley, a former governor of South Carolina; among many of them, there is intense opposition to Mr. Trump’s presidential run. And as The Washington Post points out, nearly one in five Republican primary voters across four contests on April 2 voted for an option other than Mr. Trump — even though he was the only Republican still campaigning at that point.

So two things are happening at once: The Republican Party is thoroughly MAGA and will be for the foreseeable future, and there is a small but influential number of Republicans who are deeply opposed to what their party has become but not prepared to shed their political identity and join the Democrats.

For this group, one viable course remains: create a Republican Party in exile, a counterestablishment dedicated to recapturing the party from the outside.

In world history, exiles, expatriates and their movements have played important roles in fighting unjust regimes. They bring detailed knowledge of their country and its politics to bear on efforts to change the government. They assemble agendas and personnel for its eventual replacement. They provide a rallying point and inspiration for regime opponents who otherwise might succumb to fatalism and fatigue. They connect and coordinate disparate exile factions.