Joe Biden and Bernie Sanders have been running very different kinds of campaigns, built on very different ambitions. Biden’s been running to lead the Democratic Party more or less as it exists today. Sanders, by contrast, has sought to lead a political revolution that will upend not just the Democratic Party but American politics more broadly.

On Super Tuesday, Sanders’s political revolution didn’t turn out, but the Democratic Party did.

“A big problem for the Sanders theory of this race is that when turnout is high, he wins,” writes Dave Weigel, a political reporter at the Washington Post. “Turnout is way up, but the most reliable new voters are Biden-curious suburbanites.” As election analyst Dave Wasserman noted, the new voters Sanders promised to pull into the party didn’t emerge, and as a result, he’s lost ground from 2016.

Sanders didn’t get wiped out on Tuesday night — far from it. He won Vermont, Utah, and Colorado (and likely California, though the final tallies won’t be reported for a while). But Biden surged unexpectedly to win Alabama, Arkansas, Massachusetts, Minnesota, North Carolina, Oklahoma, Tennessee, and Virginia — and as I write this, he’s narrowly favored to win Texas and Maine, too.

It’s not that Sanders is running a weak campaign. But he is, in a way, running the wrong campaign. He’s the frontrunner for the Democratic nomination — at least he was until tonight — but he’s still running as an insurgent. The political revolution was supposed to close the gap between these realities: If Sanders could turn out enough new voters, he could sweep away the Democratic establishment and build his own party in its place. But going all the way back to Iowa, that strategy failed. Sanders won as a Democrat, not a revolutionary, and he needed to pivot to a strategy that would unite the existing Democratic Party around him.

But it’s hard to move from treating the Democratic Party establishment with contempt to treating it like a constituency, and so far, the Sanders campaign hasn’t. On Tuesday, David Sirota, one of Sanders’s speechwriters, tweeted:

In recent weeks, Biden has been racking up endorsements from Democratic Party heavyweights. Days before the crucial South Carolina primary, Rep. Jim Clyburn blessed Biden — giving him the single most important endorsement a Democrat can win in South Carolina. Biden went on to win the primary by almost 30 points. Days later, Biden got endorsements from Pete Buttigieg, Sen. Amy Klobuchar, Beto O’Rourke, and Harry Reid — endorsements that, in his speech Tuesday night, he credited with helping him notch a shockingly strong Super Tuesday performance.

Sanders’s supporters have reacted to these endorsements with fury. To them, it’s proof the fix is in.

If that’s the lesson Sanders’s supporters take about how power works, it’s the wrong lesson. The work of the president requires convincing legislators in your party to support your agenda, sometimes at the cost of your political or policy ambitions. If Sanders and his team don’t figure out how to do it, they could very well lose to Biden, and even if they win, they’ll be unable to govern.

Persuading the Amy Klobuchars of the world to support you, even when they know it’s a risk, is exactly what the president needs to do to pass bills, whether that’s a Green New Deal or Medicare-for-all or just an infrastructure package. Biden, for all his weak debate performances and meandering speeches, is showing he still has that legislator’s touch. That he can unite the party around him, and convince even moderate Democrats to support a liberal agenda, is literally the case for his candidacy.

Sanders hasn’t demonstrated that same skill over the course of this primary, or his career. Worse, his most enthusiastic supporters treat that kind of transactional politicking with contempt. Senators like Cory Booker, Kamala Harris, and Elizabeth Warren, who co-sponsored Sanders’s Medicare-for-all bill but quibbled with details or wanted to soften sections, were treated not as allies to cultivate but as traitors to exile.

Similarly, Sanders’s supporters have been furious, for weeks, that Warren hasn’t dropped out and endorsed Sanders. What they haven’t done is ask why Sanders hasn’t been able to convince her — or any of the major Democrats who have already dropped out — to endorse him. Whatever case Biden is making or deals he’s offering, Sanders isn’t matching him. Or perhaps the well has been poisoned by Sanders supporters filling Twitter with tweets calling Warren a snake and the Democratic establishment a cabal.

Tellingly, what Sanders did get was Marianne Williamson’s backing, and she’s arguing that the Democrats supporting Biden are launching a coup worse than anything attempted by Russia:

This kind of thinking is a bigger problem for the Sanders operation than people realize: If you treat voters and officials in the party you want to lead as the enemy, a lot of people in that party aren’t going to trust you to lead them. It’s part of the reason Sanders trails not just Biden but also Mike Bloomberg and Warren in endorsements from prominent elected Democrats.

This is a real weakness for Sanders, and one that’ll be hard to address: That he’s an insurgent facing down a corrupt Democratic establishment is core to his identity, and to the bond he’s built with his staunchest supporters. But to win the Democratic primary and govern as a Democratic president, you need to win over Democrats who aren’t your natural allies, who didn’t start out in your corner. Biden knows that and acts accordingly. The Sanders campaign is going to have to learn the same lesson, and fast.

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Every other Saturday from now to Election Day, Vox co-founders Matthew Yglesias and Ezra Klein will sit down to discuss the most important elements of the 2020 race to the White House. Subscribe to The Weeds, Vox’s podcast for politics and policy discussions, on Apple Podcasts, Google Podcasts, Spotify, Stitcher, or wherever you like to listen.