On Wednesday evening, a hard-line Conservative minister, Robert Jenrick, resigned from the British government to protest its new immigration policy. Hours later, in Washington, Kevin McCarthy, the California Republican toppled by his right-wing colleagues as House speaker in October, announced he would resign from Congress.
A pair of bitter political exits, on opposite sides of the Atlantic, that drove home again how Britain and the United States have been lashed together in the populist storms unleashed by Brexit and Donald J. Trump. The two major right-of-center parties, Conservatives and Republicans, have become almost mirror images: Deeply divided, radicalized, and close to unmanageable for their embattled leaders.
There are differences, of course: Prime Minister Rishi Sunak clings to power as the Tory leader, partly because lawmakers cannot stomach the idea of throwing out another prime minister after Liz Truss and Boris Johnson.
Republicans, by contrast, appear firmly in thrall to Mr. Trump, the front-runner for the G.O.P. presidential nomination whom many in the party view as the best bet for recapturing the White House next year. And the vitriolic nature of the debate on Capitol Hill still makes the proceedings in the House of Commons look comparatively civil.
At times, however, Mr. Sunak resembles no one so much as Mr. McCarthy during his ill-fated nine months as speaker: Struggling to corral the moderate and extreme right factions of his party as it faces a looming election.
The revised asylum law that Mr. Sunak introduced on Wednesday — which would override Britain’s Supreme Court and disregard some human rights laws to put asylum seekers on one-way flights to Rwanda — managed to disappoint both the party’s rule-of-law centrists and its go-for-broke right-wingers.
Mr. McCarthy was never able to square that circle with House Republicans on contentious issues like averting a government shutdown. He was replaced as speaker by an even more conservative figure, Mike Johnson of Louisiana, before announcing on Wednesday that he would leave Congress a year before the end of his term.
The similarities between the Tories and the G.O.P. are registering with political analysts in Britain, who have been alert to these parallels since 2016, when the shock vote to leave the European Union presaged the election of Mr. Trump that fall. In his gleeful disregard for rules and norms, Mr. Trump was often compared to Mr. Johnson, under whom the Rwanda asylum policy was conceived.
“We are facing the fact that maybe this party has slipped its moorings as a center-right party and become a party of the populist radical right,” said Tim Bale, professor of politics at Queen Mary University of London. “Just as, if you look at the U.S., the Republican Party can’t really claim anymore to be a mainstream conservative party.”
“The Conservative Party in the U.K,” Professor Bale said, “is in danger of going the same way.”
While Brexit is in the rearview mirror, the issues that electrified that debate — immigration and British sovereignty — remain resonant. Much as Mr. Trump has used fears about migrants crossing the southern U.S. border to mobilize his base, Mr. Sunak has made stopping the flow of small boats across the English Channel an article of faith with Conservative voters, particularly in England’s north and Midlands.
Immigration is the No. 1 issue with Republican voters, according to some polls, which was evident in the unanimous vote by Senate Republicans on Wednesday to reject a bill that included aid for Ukraine and Israel, unless President Biden agreed to negotiate provisions to tighten border security.
“There’s some commonality between images from our border and those from Calais, that harden voter sentiment,” said Doug Heye, a Republican strategist and former aide to Representative Eric Cantor of Virginia, the onetime House majority leader, who was ousted in 2014 by a far-right challenger.
In Britain, Conservatives fear being outflanked on their right by Reform U.K., a fringe party and successor to the Brexit Party which was led by Nigel Farage, who turned immigration into an emotive issue in the years before the referendum on leaving the European Union. Nowadays, Mr. Farage likes posting images of people landing on the beaches of Kent in inflatable dinghies.
Conservatives are also seizing on immigration to draw sharp differences with the opposition Labour Party, which holds a double-digit lead in polls. But analysts said Mr. Sunak’s attempts to exploit border security in the general election, which he must call by January 2025, have backfired because a faction of his party now seems to view the issue in ideological, rather than pragmatic, terms.
“Every single Conservative leader since David Cameron has found the same thing,” said Professor Bale, referring to the former prime minister and current foreign secretary, who resigned after the British electorate voted for Brexit, a policy he had campaigned against. “They believe they can use this issue as a way of creating dividing lines with Labour, but they end up turning the gun on themselves.”
For Mr. Sunak, that journey has been particularly abrupt. After his government’s Rwanda plan was rejected by the Supreme Court as being in breach of British and international law, Mr. Sunak vowed to revise it. The new legislation declares that Rwanda is a “safe country” for asylum seekers, contradicting the court and evidence it received from the United Nations refugee agency, and stipulates that no court will have authority to block transfers.
“This is a very extreme act,” said Jonathan Sumption, a historian and former justice on the Supreme Court. “It effectively sidelines the courts, with very limited exceptions. I didn’t expect them to go as far as they did.”
And yet, it did not go far enough for Mr. Jenrick, the immigration minister who turned in his resignation. He had pressed for Britain to be willing to withdraw from the European Convention on Human Rights, which it helped draft in the aftermath of World War II. Centrist lawmakers fear that the policy would make Britain a scofflaw.
The legislation goes to a vote on Tuesday, and if Mr. Sunak loses the backing of 29 Tory rebels, he could face not only a stinging repudiation of a flagship policy but also a crippling blow to his authority.
On Thursday, Mr. Sunak said of his critics, “the difference between them and me is an inch,” and cast the upcoming vote as a chance for “Parliament to demonstrate that it gets the British people’s frustration.”
The disarray in the Conservative Party has even revived talk of a challenge to Mr. Sunak’s leadership, not unlike the one Mr. McCarthy faced.
Having switched leaders twice last year and four times since 2016, the Tories have proved ruthless at ridding themselves of prime ministers who appear destined to lead them to electoral defeat. But doing so again would severely test the patience of the British public and fuel calls for a swift general election.
The fact that a challenge is even being discussed reflects the pervasive gloom in Tory ranks after a year in which Mr. Sunak made a string of policy and personnel changes, none of which have improved his party’s dire poll ratings.
“Voters in the U.K. are more civil and respectful to people they disagree with, but the same ideological chasm and political poison within and among the electorate is apparent on both sides of the Atlantic,” said Frank Luntz, a Republican strategist who has studied the British political system.