Democratic presidential candidate, former U.S. Vice President Joe Biden, in Algona, Iowa | Scott Olson/Getty Images Joe Biden warns that Boris Johnson’s victory shows dangers of parties leaning too far left The leading 2020 contender told donors that the UK election holds lessons for the White House race.

Former U.S. Vice President Joe Biden on Thursday sought to draw parallels between the results of the United Kingdom’s general election and the 2020 White House race — arguing that British Prime Minister Boris Johnson’s resounding victory should warn Democrats against veering too far left in their fight to defeat President Donald Trump.

“Boris Johnson is winning in a walk,” Biden, a leading Democratic presidential candidate, told attendees of a campaign fundraiser in San Francisco. The prime minister’s Conservative Party captured an overwhelming parliamentary majority in Thursday’s election, taking dozens of seats in Britain’s House of Commons from opposition leader Jeremy Corbyn’s Labour Party.

Predicting news headlines reporting the thumping by Johnson’s Tories, Biden said: “Look what happens when the Labour Party moves so, so far to the left. It comes up with ideas that are not able to be contained within a rational basis quickly.”

Biden went on to assert that the prime minister’s triumph would change public perceptions regarding Trump’s odds of re-election. “You’re also going to see people saying, ‘My God, Boris Johnson, who is kind of a physical and emotional clone of the president, is able to win,'” he said.

Biden has advanced a more moderate political ideology throughout the Democratic primary, criticizing sweeping policy proposals from the field’s leading progressive contenders, Sens. Bernie Sanders of Vermont and Elizabeth Warren of Massachusetts.

The vast majority of the party and the broader electorate, Biden has claimed, are not as liberal as those candidates would suggest, and instead are seeking a sense of national unity in a post-Trump era and a restoration of America’s role on the world stage.

Some of Biden’s rivals have slammed his appeals for bipartisanship as naive and outdated given the rancor of Washington and levels of animosity between Democratic and Republican lawmakers. But Biden pushed back against that critique Thursday, charging that “there’s not a single candidate running who has ever passed a major piece of legislation” in Congress.

Biden insisted that while his competitors employ a “completely different style,” he never questions others’ motives and always attempts to find common ground. “Presidents are supposed to be able to persuade and work something out,” he said, adding that he thinks he has “been relatively good at doing that.”