Labour Party leader Jeremy Corbyn leaves Labour headquarters on Friday in London. (Chris J Ratcliffe/Getty Images)

Early Friday morning, as he grew confident that Britain’s ruling Conservative Party had lost its parliamentary majority, Labour Party leader Jeremy Corbyn said that he’d been proven right.

“Politics has changed,” Corbyn told voters in Islington, his parliamentary constituency, after he won by a bigger-than-expected landslide. “Politics isn’t going back into the box where it was before. What’s happened is people have said they’ve had quite enough of austerity politics.”

An ocean away, Sen. Bernie Sanders (I-Vt.) was watching the results, and seeing what Corbyn saw — a strong Labour performance, with surging turnout, and seats that had not been expected to change hands being flipped by newly registered young voters.

“I am delighted to see Labour do so well,” Sanders told The Washington Post in an email. “All over the world people are rising up against austerity and massive levels of income and wealth inequality. People in the U.K., the U.S. and elsewhere want governments that represent all the people, not just the 1 percent. I congratulate Jeremy Corbyn for running a very positive and effective campaign.”

Sanders had company. For the American left, Corbyn’s campaign had been an unexpected thrill ride, and a partial vindication of populist, redistributive politics. After Donald Trump, no politician in the English-speaking world had been so frequently accused of wrecking his party. No major left-wing politician had been so often accused of being unelectable — not even Sanders. Polls going into Election Day had forecast a tough but decisive reelection for Prime Minister Theresa May.

“The parallels to Bernie Sanders are obvious,” said David Axelrod, the former Obama strategist who went on to advise the Labour Party in its 2015 defeat, in an email before the vote. “You saw a surge of youth voting, in response to a very progressive agenda and a very unorthodox but authentic candidate. The agenda — more social spending; higher taxes on the wealthy — was galvanizing. The style — open and seemingly honest — was a stark contrast with May’s tight-lipped, no-risk approach.”

All through election night, the BBC and other organs of an infamously Corbyn-skeptical media marveled at how Labour had gained ground. May’s disastrous campaign was part of the reason; Trump’s decision to spar with Sadiq Khan, the popular Labour mayor of London, didn’t help. But Corbyn’s many critics, who had tried to remove him from power or quit his shadow cabinet, took turns eating crow and admitting that he’d changed the electorate.

“His own party tried to remove him!” Sanders marveled in a short interview before the polls closed. “They were stopped at the grass-roots level. He registered hundreds of thousands of new voters. It’s an incredible thing.”

The unavoidable conclusion was that Conservatives ran on cold austerity, and Labour ran on what the media nicknamed a “giveaway” manifesto, with a higher minimum wage, free college tuition, re-nationalization of some public goods, and new public housing, paid for by new taxes on the very wealthy. Turnout by voters under 25 grew, by some reports, to nearly three-quarters. Seemingly safe conservative constituencies, like Canterbury, flipped thanks to student turnout. The author of the Conservative platform lost his own seat, credited to a policy backlash.

“Labour’s surge confirms what the Left has long argued: people like a straightforward, honest defense of public goods,” wrote Bhaskar Sunkara, editor of the socialist magazine Jacobin. “The Labour left remembered that you don’t win by tacking to an imaginary center — you win by letting people know you feel their anger and giving them a constructive end to channel it towards.”

On Twitter, the release of the exit poll that showed May losing her majority kicked off hours of celebration. Much of it echoed Sunkara; other contributors to Jacobin celebrated how Corbyn had proven that left politics could actually win, and that organizers didn’t have to settle.

Will Menaker, a co-host of the popular leftist Chapo Trap House podcast, was one of the loudest voices in a chorus shaming center-left pundits and Democrats for doubting that Sanders could have won the presidency.

The actual results, which left Labour with just 261 of 650 seats in the House of Commons, did not actually put the left in power. But in several other ways they validated what the left in Britain and the United States had been arguing since 2015, when Sanders gained ground in the Democratic primary and Corbyn won the Labour Party’s leadership. Corbyn, who had been elected to eight terms but never served in leadership, argued that the “New Labour” politics that had last put the party in power had ended in disaster, with a de-motivated electorate blurring distinctions between parties and putting the Conservatives in power.

“The media and many of us, simply didn’t understand the views of young people in our country,” Corbyn said when he won the leadership. “They were turned off by the way politics was being conducted. We have to and must change that … I say to those returning to the party, who were in it before and felt disillusioned and went away: Welcome back, welcome home.”

From the outset, polls suggested that Corbyn, who had a long and public record of left-wing and anti-interventionist views, could not win a general election. He consistently trailed both former prime minister David Cameron (who resigned after Brexit) and May when voters were asked who’d be the best prime minister. Interviews often foundered on questions of whether he let anti-Semitism flourish in the party, whether he’d tell police not to shoot terrorists in hostile situations, and why most of his party had voted in 2016 to hold a new leadership election in the hopes he’d lose. (They did; he didn’t.)

Corbyn began the 2017 general election just as mired, with polls suggesting that Labour could fall below 30 percent of the popular vote and give May — in a commonly repeatedly headline shorthand — “the biggest Tory landslide since Thatcher.” Even as Corbyn’s Labour gained in the polls, most newspapers endorsed the Tories; a national town hall meeting featured seven minutes of voters asking why Corbyn wouldn’t favor a nuclear retaliation if the nation was attacked. The Tories’ strategy, which was partially based on Corbyn’s perceived toxicity, sent them into working class areas where the United Kingdom Independence Party had surged, on a bet that voters would leave that collapsing party to back May’s “strong and stable” approach to Brexit.

For the most part, they didn’t — and where they did, Labour often found new voters to replace them. Corbyn, waging a Sanders-like campaign of massive rallies and voter registration, drove the total Labour vote to nearly 13 million (12,858,644 as of Friday morning), and around 40 percent of the total. That was the highest pure vote for Labour since 1997, when Tony Blair won his first landslide; it was the largest swing toward the party from one election to the next since 1945, when Clement Attlee’s Labour used a post-World War II mandate to create most of the country’s social insurance programs.

It also represented a slide for Britain’s center-right and right-wing parties. In 2015, the Conservatives won a majority with 36.9 percent of the vote, as UKIP won 12.6 percent, totaling 49.5 percent. On Thursday, the combined Tory/UKIP vote was just 44.3 percent; the combined vote for Labour, the leftish (and anti-Brexit) Liberal Democrats, the leftish Scottish National Party, and the Green Party was 52 percent.