In our age of extreme polarization, a widespread school of thought holds that swing voters are nearly extinct, and that turnout is everything. But that’s an exaggeration. While there seem to be fewer swing voters than in the past, they can still be decisive.

As Ruy Teixeira, a senior fellow at the Center for American Progress, pointed out in The Washington Post, the 2018 elections saw the highest midterm turnout in over a century, yet most of Democrats’ improved performance “came not from fresh turnout of left-of-center voters, who typically skip midterms, but rather from people who cast votes” in the last two national elections and “switched from Republican in 2016 to Democratic in 2018.”

The primaries have yet to demonstrate that Sanders can generate the hugely expanded turnout his campaign is promising, though that could change when the Super Tuesday results come in. In New Hampshire, turnout increased most in the places that voted for Pete Buttigieg and Amy Klobuchar.

Dave Wasserman, an editor at The Cook Political Report, tweeted that most of the Democrats’ turnout bump was attributable to moderate Republicans “crossing over from ’16 G.O.P. primary — not heightened progressive/Sanders base enthusiasm.” South Carolina saw record turnout, but it benefited Biden, not Sanders.

None of this means that Democrats would be justified in denying Sanders the nomination if he arrives at the convention with a strong plurality of delegates. Doing so would tear the party apart, probably leaving the eventual nominee even less electable than Sanders is. But it does mean that if Sanders wins the primary, his campaign has to learn to persuade people, not just mobilize them.

College-educated white women, for example, helped flip the House in 2018. They favor Biden over Trump by double digits, but Sanders by only two points. Sanders, however, seems to see little need to reach out to them. Speaking to The Los Angeles Times editorial board in December, Sanders said he didn’t believe the way to win against Trump “is to just speak to Republican women in the suburbs.”

Instead, he said, “The key to this election is, can we get millions of young people who have never voted before into the political process, many working people who understand that Trump is a fraud, can we get them voting?” Even if the answer is yes, it probably won’t be enough. If he’s going to be the nominee, the rest of us can only hope his campaign has a Plan B.