LONDON — Britain was still counting the final votes in its landmark general election early Friday morning when Democrats and Republicans on the other side of the Atlantic began speculating whether Prime Minister Boris Johnson’s landslide victory was a good omen for President Trump’s re-election chances in 2020 — and a cautionary tale for Democrats.
It had happened before, in 2016, when Britain’s angry vote to leave the European Union came to be seen as a canary-in-the-coal-mine for Mr. Trump’s insurgent victory over Hillary Clinton five months later. And on Friday in the Oval Office, Mr. Trump seized on the idea that history might repeat itself.
“I think that might be a harbinger of what’s to come in our country,” he said of Mr. Johnson’s big victory.
But if there are parallels, there are also important differences between this British election and the American one next year.
The populist contagion that defined the 2016 elections has not dissolved in either country but the dynamics are different. Mr. Johnson appealed to populist anger but he also seized on a sense of nationwide exhaustion with Brexit, a desire to break the political deadlock and, as he put it, “Get Brexit Done.”
Mr. Trump cheered on Mr. Johnson from the sidelines, even as the British leader desperately tried to keep a distance from the American president. But there are key differences between Mr. Trump and Mr. Johnson: The American president’s disruptive style and deep unpopularity with large segments of the electorate, even brought some comparisons with Jeremy Corbyn, the vanquished Labour leader, rather than with the breezy Mr. Johnson.
For all his populist bluster, Mr. Johnson rejected a proposal to join forces with the hard-right Brexit Party, calculating he could win a Parliamentary majority without its help. In victory, he has appealed for British unity with promises of funding for schools and the National Health Service, a big-government approach that would not look out of character for a European Social Democrat.
For Republicans, who have fully embraced Mr. Trump, Mr. Johnson’s victory shows not just the continuing potency of populism but also its limits. For Democrats, who have been engaged in a battle between their progressive and moderate wings, the Labour Party’s defeat is, on one level, a useful example, since party officials have long debated the risks of tacking to the left. Still, there is no equivalent among Democrats running for president to Mr. Corbyn, who is a deeply divisive figure.
“There’s going to be a huge debate about why Labour lost, which has ramifications in the United States,” said Thomas Wright, director of the Center for the United States and Europe at the Brookings Institution.
“Some Democrats will say it lost because Corbyn was unpopular and the party had an anti-Semitism problem,” Mr. Wright said. “Others will say the party’s left-wing economic policy was the problem.”
Joe Biden, the leading moderate Democrat in the presidential race, lost no time making the latter case. Speaking at a fund-raiser in San Francisco on Thursday, he predicted that the Labour loss would be chalked up to its extreme positions.
“Look what happens when the Labour Party moves so, so far to the left,” Mr. Biden said, characterizing the analysis he expected. “It comes up with ideas that are not able to be contained within a rational basis quickly.”
It was a not-so-subtle plea to Democrats to choose him over liberals like Senator Elizabeth Warren of Massachusetts or Senator Bernie Sanders of Vermont. Mr. Johnson’s victory, Mr. Biden said, would also be interpreted as promising for Mr. Trump, since he is “kind of a physical and emotional clone of the president.”
Given the historically close ties between the United States and Britain, it is telling that this election was characterized more by the distance those on each side kept from the other. Mr. Johnson played down his friendship with Mr. Trump, pleading with the president not to intervene in the election during his visit to a NATO meeting in London in the days leading up to the vote.
Mr. Trump is such a radioactive figure in Britain that the Conservatives feared his public endorsement would backfire on the prime minister. Until his congratulatory tweets on Thursday evening, Mr. Trump largely complied.
On the Democratic side, liberal figures like Ms. Warren and Mr. Sanders kept Mr. Corbyn at arm’s length — a reflection, analysts said, of the accusations of deep-rooted anti-Semitism in the Labour Party, as well as the belief that he was not going to do well. Among prominent Democrats, only Representative Alexandria Ocasio-Cortez, Democrat of New York and a supporter of Mr. Sanders, publicly endorsed Mr. Corbyn’s party. (A top official in Mr. Sanders’ campaign, however, also posted a message of support Thursday on Twitter. )
Stephen K. Bannon, former chief strategist to Mr. Trump, contends that the president’s victory in 2016 was “inextricably linked” to the Brexit vote. He views Mr. Johnson’s success as revealing deeper political currents that could threaten the chances of the Democratic nominee in 2020.
“It’s not just about Corbyn,” he said. “If they don’t grasp the reality of the rejection of the program of Corbyn, they’re going to get a brutal lesson.”
But Mr. Bannon said the election also held lessons for populists on the right. Mr. Johnson’s rebuff of the Brexit Party, which had proposed campaigning together on a hard-line, pro-Brexit platform, will free the prime minister to try to draw the Conservative Party back to the political center.
“You will see a limited appetite for populism in the Tory party,” Mr. Bannon said. “They see that they didn’t need it.”
Some British analysts dismissed the argument that Labour’s loss was a repudiation of its agenda, saying that some of its proposals, like increased funding for the National Health Service, were popular with much of the electorate. The problem, they said, was the party’s standard-bearer.
Mr. Corbyn’s hard-left ideology makes Ms. Warren look moderate, political analysts said, while Mr. Sanders is far more personally popular than the Labour leader. The Sanders campaign has calculated that by moving left, it can mobilize a multiracial working-class coalition, while at the same time luring back rural white voters.
To some Democratic strategists, the Labour Party represents the worst-case scenario of that gamble: Moving left did not retain working-class voters in the British Midlands and the north — the party’s bedrock support — but drove off center-left professionals in the south of Britain, who voted to stay in the European Union.
Still, Anand Menon, a professor of European politics at King’s College in London, said, “Bernie Sanders is an infinitely more effective politician than Jeremy Corbyn.”
For Democrats, there are tactical lessons in Labour’s defeat. Mr. Johnson ran a highly disciplined campaign, pounding home his message that he would “Get Brexit Done” and avoiding debates over kitchen-table issues, like health care, which could have played to the advantage of Labour.
“It shows the importance of discipline,” Mr. Menon said. “There was a simplicity of message.”
Mr. Johnson also successfully framed his campaign as a revolt against Britain’s political establishment. Parliament, he said, had thwarted the democratic will of the people in not delivering Brexit. The prime minister bludgeoned Mr. Corbyn for his muddled position on Brexit.
Mr. Trump is likely to use a variation on the people vs. the establishment narrative, attacking Democrats in Congress, who are on track to impeach him, for trying to thwart the will of the voters who elected him in 2016.
As in the United States, Britain’s election was characterized by extraordinary rancor and a blizzard of dubious claims from the candidates. And, as in the United States, the peculiarities of the British political system guaranteed that the winner was not the party that got the most votes.
While Mr. Johnson’s Conservatives won a 79-seat majority in Parliament, they and the other pro-Brexit parties drew only 46 percent of the vote. The Labour Party, and other parties that either oppose Brexit or want to rethink Britain’s departure, won 52 percent. Britain’s first-past-the-post system — meaning that in each constituency, the candidate who gets the most votes wins, regardless whether that’s a majority — allowed the Conservatives to win a disproportionate share of seats.
This has prompted debates about overhauling the electoral system that echoed the calls for reform after Mr. Trump defeated Mrs. Clinton in the Electoral College, despite losing to her by 2.8 million votes. And like in the United States, there seems little prospect of changing the system any time soon.
Alexander Burns contributed reporting from New York, and Jonathan Martin from Washington.