Defying all expectations, Jeremy Corbyn has led the Labour Party in the United Kingdom to a stunning turnaround from guaranteed loser to genuine contender in Thursday’s election.

Though still very much the underdog, Corbyn has reinvigorated the party with a surge of youthful, socialist enthusiasm that will look familiar to anyone who followed last year’s Democratic presidential primaries. And that success could provide a guide for Democrats looking to build their party up in the age of Trump.

Corbyn and the Labour Party he leads were supposed to lose the U.K. election, and badly.

Polling in April, when Prime Minister Theresa May called the snap election, showed May’s Conservative Party with a nearly 20-point lead. But days before the election, polling averages have put the Tory lead down to around 7 points, with one recent poll giving them a lead of just a single point.

What’s remarkable, according to several analysts following the election, is how great of an effect Corbyn’s surge could have on both British and American politics, even if he doesn’t end up becoming prime minister. 

That’s because he ran unapologetically on the socialist policies that the rest of his party spent the last couple of decades running away from. He’s elevated his party’s younger, more enthusiastic base that has clamored for far more liberals policies than party leadership had been willing to offer. 

“Corbyn illustrates that popular frustrations can go left or right,” said Robert Kuttner, co-editor of the liberal American Prospect. “Neither Corbyn nor [Sen. Bernie] Sanders is an ideal leader, but in both cases, they did much better than expected and it shows there’s latent politics waiting for the right leadership.” 

Feeling the Bern

Those elements of Corbyn’s rise invite obvious comparisons to Vermont independent Sen. Bernie Sanders’ run for president last year.

“Both are older leftists who weren’t a part of the establishment parties’ move to the center in the ’80s and ’90s, they’ve been backbenchers and gadflies their whole political careers,” said Marshall Steinbaum, senior economist at the Roosevelt Institute, a liberal think tank.

When Sanders ran on “Medicare for All,” free public college, and a $15 minimum wage, there wasn’t a lot of research and analysis to back those proposals up, Steinbaum said, because even liberal think tanks didn’t consider them popular or realistic.

That’s changed, as “Medicare for All” has especially energized the Democratic base, against objections from party leadership.

The affinities aren’t lost on Sanders. He campaigned for Corbyn in the U.K. last week, noting that “there is a real similarity between what he has done and what I have done — he has taken on the establishment of the Labour Party and gone to the grass roots. … That is exactly what’s taking place in the United States and what I’m trying to do with the Democratic Party.”

Dean Baker, co-director of the left-leaning Center for Economic and Policy Research, pointed out another similarity between the two.

“Neither was thought to be prime minister or president material,” he said. “They don’t have the background that a [Hillary] Clinton or [John] Kerry does, so in addition to their politics being left-wing, there’s also a style where they’re not the kind of people you envisioned holding the top position.”

Sanders attracted some voters with his pointed plain-spokenness, but few would have expected a largely youth-driven movement to coalesce around a politician who’s been frequently described — even self-described — as cranky and grumpy. Corbyn has been more critically described as “rigid, awkward, and utterly without charisma,”  with many citing his awkward personal style as a key reason for Labour’s initial poor polling. 

Policy moves

Corbyn unveiled an ambitious party manifesto in May that many have credited as a major part of his success.

“It’s not a lot of wonky stuff,” Kuttner said. “It’s big stuff: Let’s raise taxes on the top 5 percent and corporations, let’s spend money to restore free college tuition, renationalize the rail system that’s been privatized. It’s big, thematic stuff people can get their minds around.”

That’s in comparison to policies from Democrats and previous Labour governments, which, Kuttner said, “you have to be from the [Government Accounting Office] to understand. … It’s not compelling politics.”

Baker said he has “serious reservations” about quickly phasing in a $15 dollar minimum wage as Sanders proposed, but added that “it’s a big thing, and people understand that. Put it out there, and people hear it.”

“He’s even to the left of Sanders,” Kuttner said of Corbyn, “on the Middle East, and on whether Britain should be a nuclear power. Yet economic issues are so powerful, he’s doing well.”

Kuttner said there was also an element of “luck of the draw” in Corbyn being up against May. 

“May is reminiscent of Hillary,” he said, “running a wretched campaign, very complacent, going from one mistake to another.” Meanwhile, even those who don’t necessarily agree with him “have grudging respect for Corbyn, like Sanders, because he seems to have integrity,” Kuttner said.

“I say this all as someone who’s not a particular fan of Corbyn,” Kuttner said. “As recently as two months ago, I was in the group that said this was the death knell of the party. I’m as surprised as anybody.”

Key to Corbyn

Steinbaum said Corbyn’s rise was a sign of the “continued breakdown of the policymaking consensus of 1978-2008.” In that period, the Labour Party moved from the left to the center, “disciplining its own trade union constituency, which was very powerful,” and accepting more of the Margaret Thatcher-led consensus that austerity and shrinking the government were answers to the U.K.’s problems.

Democrats in the U.S. followed a similar path, as they went from the party of the New Deal and the Great Society to the party that wanted to “end welfare as we know it” in President Bill Clinton’s famous words. 

Since the 2008 economic crisis, Steinbaum said, that Labour consensus has been eroding, with previous Labour leader Ed Miliband attempting to “thread the needle between proposing radically different policy and broadly accepting the critique” that austerity was still the answer.

Even after the 2015 election resulted in Labour’s largest defeat since 1987 and led to Miliband stepping down, the party’s leadership largely stayed the course on policy.

That set the stage for Corbyn’s emergence as party leader, a widely unexpected turn of events. Labour lowered the fee required to vote in its leadership election, allowing younger, poorer, and less engaged voters to participate. He became Labour leader with their support, over strident objections and an attempt to remove him by many of the party’s members of Parliament (which some have compared to the bias shown against Sanders by Democratic Party officials in the primaries last year).

Parliamentary hopes

While Corbyn has clearly had an effect on U.K. politics so far, hardly any are expecting the Labor Party to gain a majority on Thursday. 

Steinbaum said there was a 70 percent probability that May’s Conservatives would still win a majority — though a much smaller one than anyone would have expected in April — and keep control of government.

After a defeat, the losing party’s leader typically resigns, though Corbyn could also choose not to, or he could “resign in a position of strength,” as Steinbaum put it, having given credence to his platform with better-than-expected results.

But Steinbaum also said there was a 30 percent chance that no party will win a majority, resulting in a hung Parliament. That would result in complicated political maneuvering, likely ending with Corbyn as prime minister.

Baker said that while the U.S. is often so focused on American politics that international political events don’t sink in, “there’s a closer affinity with the U.K. than with other countries. It’ll be big in the news if there’s a hung Parliament.”