U.K. Independence Party leader Paul Nuttall speaks to supporters on May 20 as he campaigns with the party’s parliamentary candidate in Clacton-on-Sea, in eastern England. (Chris J. Ratcliffe/AFP/Getty Images)

It was a night beyond all compare. 

Less than a year ago, Britain voted to get out of the European Union. And as the country’s new destiny dawned in the early hours of June 24, veteran activists of the U.K. Independence Party — an anti-E.U. movement long derided as extremist — felt the sweet satisfaction of having forced the referendum and steered the national debate with their anti-immigration rhetoric.

“Twenty-one years of being called a closet racist or a swivel-eyed loon,” said Tony Finnegan-Butler, a party activist since UKIP was born in the mid-1990s who is now the party’s chair in Clacton-on-Sea, a pro-Brexit stronghold. “And one night you learn that more than half the population thought you were right in the first place.” 

But if the vote brought vindication, it has not ushered UKIP any closer to political power. In fact, exactly the opposite. 

(Sarah Parnass,Griff Witte/The Washington Post)

What happens to far-right populist movements when their fondest dreams come true? If the experience of UKIP is any guide, the answer is that they fall apart.

A year after achieving its most sacred ambition, the party long led by President Trump’s favorite European politician, Nigel Farage, is in disarray, scarred by prominent defections and by vicious feuding — some of it physical — among its remaining members. An election on June 8 in which the party’s share of the vote is expected to crater may be UKIP’s death blow.

The arc of UKIP’s story — years of obscurity followed by one astonishing success and now a rapid and possibly terminal decline — illustrates one way of blunting the appeal of populist movements: Give them exactly what they want.

“We’re suffering for our success,” said Finnegan-Butler, 73, who acknowledged that even he is wavering on whether to continue backing the party.

But UKIP’s sudden decline also demonstrates the degree to which right-wing populists have shifted the European policy debate toward their turf. If UKIP is losing support, it is not because the party’s ideas have lost favor. It is because mainstream parties have co-opted their causes and adopted their rhetoric.

“We’re happy that the UKIP vote is going down. But we’re not celebrating,” said Nick Lowles, chief executive of the London-based anti-extremism group Hope Not Hate. “If anything, it’s the worst of all outcomes, because we’ve seen the mainstreaming of these views that were once considered beyond the pale.” 

It’s not just in Britain, where Prime Minister Theresa May, a Conservative, sounds every inch the die-hard Brexiteer with her pledges to carry out a hard break with Europe.

Across the continent, mainstream politicians are attempting to beat back the far-right wave by mimicking the language and policies of the populists on hot-button issues such as immigration, cultural identity and Islam.

In the Netherlands, Prime Minister Mark Rutte fended off a challenge from anti-Muslim leader Geert Wilders this spring using the slogan “Act normal or go away” — a phrase widely seen as a firm line on Dutch tolerance toward newcomers. 

In Austria, both major mainstream parties have sharpened their tone on immigration ahead of elections this fall that the far-right Freedom Party could win. 

Even German Chancellor Angela Merkel — a favored boogeyman of the far right because of her welcoming policies toward refugees — has endorsed a ban on burqas “wherever legally possible” as she confronts a challenge from her right flank. 

UKIP supporters gather outside a pub in Hartlepool, England, ahead of a visit by party leader Paul Nuttall in April. (Ian Forsyth/Getty Images)

But nowhere in Western Europe is the mainstream’s acceptance of the populist right’s agenda more complete than in Britain. And nowhere has the collapse of support for a populist right party been more complete. 

For much of its nearly quarter-century existence, the U.K. Independence Party was the equivalent of a rounding error in British political life. With its single-minded devotion to a seemingly quixotic goal — an E.U. exit — UKIP struggled to capture more than a couple of percentage points in national elections. 

Future prime minister David Cameron famously dismissed the party as a band of “fruitcakes, loonies and closet racists.”

But amid a surge in immigration following the E.U.’s expansion into Eastern Europe, UKIP suddenly became a major player in 2014, topping British elections for the European Parliament that spring.

Later that year, UKIP gained its first seat in Britain’s Parliament after Clacton’s Conservative representative, Douglas Carswell, defected to the insurgent party and won a special election.

Nigel Farage, shown at a pub in Sittingbourne, England, during the Brexit campaign in 2016, resigned as UKIP leader shortly after the vote to leave the European Union. (Chris J. Ratcliffe/AFP/Getty Images)

The bombastic, beer-swilling Farage crowed that “the UKIP fox is in the Westminster henhouse” and promised that other anti-E.U. Tories in Parliament would soon turn predator rather than risk becoming prey. 

In the end, there was only one more defection. But Cameron had been nervous enough about UKIP’s rise to double down on promises that the country would hold a referendum on E.U. membership if his Conservative Party won the national election in 2015. 

It did (UKIP placed third, with 13 percent of the vote), and the referendum campaign was on.

When, against all odds, the nation opted for Brexit, it would have seemed that UKIP’s moment had finally arrived. But perhaps sensing it had already passed, Farage abruptly quit as party leader just days after the vote. 

Since then, UKIP has cycled through leaders and would-be leaders — including one who collapsed and had to be hospitalized after a fight with a party rival at the European Parliament. 

Meanwhile, the Conservative Party quickly coalesced behind a successor to Cameron — May — who, despite having campaigned against Brexit, took to the cause with the zeal of a convert. 

She has repeatedly promised a hard break with the E.U. — one that will leave the country outside the single market, the customs union and the European Court of Justice.

May has also vowed to be “a bloody difficult woman” in negotiations with European leaders — a suggestion that sent a shiver of excitement through the hearts of even the most devoted Ukippers, as the party’s stalwarts are known.

“Unlike every other prime minister we’ve had, she’s willing to say no to Europe,” said Finnegan-Butler, a courtly retiree who sailed the world with the British merchant marine. “The more I listen to Mrs. May, the more I trust her.”

His car is emblazoned with a placard stating in bold purple letters: “I’m voting for UKIP.” 

But if he weren’t the party’s local chairman, he said, he probably wouldn’t.

In this pretty but faded seaside region of pebble beaches and long London commutes — the only area that UKIP won in the 2015 parliamentary elections — it seems that few others are backing the party, either.

Carswell, the party’s former representative here, quit UKIP in March after a spectacular falling-out with Farage. In his place, the party drafted a candidate with no ties to the area and, as UKIP support nationally drops below 5 percent, virtually no prospects for success.

Instead, the seat is almost certain to be claimed back by the Conservatives, whose candidate reflects the party’s drift toward pro-Brexit evangelism under May. 

Before last year’s referendum, Giles Watling was an ardent advocate for keeping Britain in the E.U.. But like the prime minister, he has reversed course since discovering that the country disagreed.

The candidate, a charismatic, 64-year-old actor turned politician who is known to voters for his roles on stage and screen, campaigns on the need to give May the strongest possible hand as she heads into contentious exit talks with her soon-to-be-former counterparts in the E.U.

“It’s a fight that we needn’t have had,” Watling said. “But it’s there, and we can win it.” 

Among those lured back to the Tory fold by that message is Valerie Grove, a retired civil servant who strayed into the UKIP column in 2014 after a lifetime of voting Conservative.

It’s not that her views have changed. She is still adamantly against the immigration that she says is “changing our entire way of life.”

“I don’t want to live in a country where there’s a mosque on every corner,” Grove said. “It’s not the British way.” 

But she feels at home again with the Conservatives, led by a prime minister who, Grove said, understands the need to control immigration. And unlike UKIP, she said, the Tories can actually deliver. 

“I was a little skeptical of Theresa May,” Grove said. “But my goodness. She’s proven that she’s got what it takes.” 

Not everyone is convinced. On a recent warm spring day, UKIP candidate Paul Oakley — a pinstripe-suited London lawyer who was brought into Clacton to run at the last minute amid intraparty feuding over who should replace Carswell — acknowledged that he is likely to lose.

UKIP candidate Paul Oakley, second from left, talks with a voter in Clacton-on-Sea. He is running to replace a member of Parliament who defected from the Conservative Party to UKIP, then quit his new party. (Griff Witte/The Washington Post)

But as he campaigned in Jaywick, a neighborhood of tattered seaside bungalows that is among the poorest in Britain, he made his best case for why UKIP still matters.

“The referendum was D-Day. It wasn’t the fall of Berlin. People can’t sit back and assume that we’ve won,” he said. “It’s all very well to sound like UKIP. But Theresa May and Giles Watling voted to remain. We can’t trust people like that to deliver a proper Brexit.”

Indeed, even as he takes a break from running for office — he has lost seven campaigns for Parliament — Farage has been singing the same tune on his radio talk show, warning of the “Brexit betrayal” to come. 

Whether Farage returns to UKIP or builds a new party, political observers say it is likely he will have ample material to launch a comeback.

Farage and UKIP may have helped sell a majority of British voters on the promise that getting out of the E.U. will solve the nation’s ills. But now that May and the Conservatives are delivering on those sky-high expectations, disappointment is almost certain to follow.

“Theresa May can’t satisfy everyone,” said David Cutts, a political science professor at the University of Birmingham. “There’s still a role there in British politics for the populist right.”

Karla Adam in London contributed to this report.