ancy Pelosi is worried about 2020. As, of course, is every Democrat, but Pelosi has an analysis of the challenge the party faces that is striking in how tentative it sounds, even frightened. Here's what she told The New York Times over the weekend:

Sitting in her office with its panoramic view of the National Mall, Ms. Pelosi—the de facto head of the Democratic Party until a presidential nominee is selected in 2020—offered Democrats her “coldblooded” plan for decisively ridding themselves of Mr. Trump: Do not get dragged into a protracted impeachment bid that will ultimately get crushed in the Republican-controlled Senate, and do not risk alienating the moderate voters who flocked to the party in 2018 by drifting too far to the left.

“Own the center left, own the mainstream,” Ms. Pelosi, 79, said.

It wasn't that long ago that Pelosi was supposed to epitomize the left’s radicalism, a “San Francisco liberal” who filled every heartland American with rage and disgust. Now she's telling the Democratic Party that the path to victory is by limiting conflict with Donald Trump and offering a sedate policy centrism.

She's not the only one. The current front-runner for the Democratic presidential nomination, Joe Biden, is basing his candidacy on the proposition that he will be able to win over significant numbers of Republican voters, once they see that he's more moderate than other Democrats and realize what a repellent human being Donald Trump is.

The only problem with that theory is that there is no reason to believe it's true. Trump’s approval from Republican voters is at a near-perfect 90 percent, according to Gallup, and it isn't like they haven’t gotten a good enough look at him to realize who he is. Their elected officials have proven time and time again that there is literally nothing Trump could do that would make them turn their backs on him; the one or two who felt that they might, like former Senator Jeff Flake, did it only when they were on their way to retirement.

But Joe Biden has faith in the GOP. “This is not the Republican Party,” he says, testifying to his bond with “my Republican friends in the House and Senate.” Once Trump is gone, they’ll revert to their old responsible selves and become reasonable again. Just like they were when Biden was vice president and they pursued a strategy of total opposition to everything Barack Obama wanted to do, capping it off by refusing to allow his nomination to a vacant Supreme Court seat to even get a hearing. Those Republicans are the ones who are supposedly going to join with President Biden in a spirit of bipartisan compromise to do what is best for the country.

While Biden has no excuse for his absurdly deluded beliefs about how Republicans would act if he were president, at least his belief about how to win a national election has a logic to it. It says that you have to persuade voters in the middle (and across it) in order to win, showing the largest number of voters that you're ideologically closer to them than your opponent.

It’s called the Median Voter Theorem (since the idea is to position yourself closer to the median voter than your opponent), and though it makes a kind of intuitive sense, in practice it usually turns out to be wrong. That’s because ideology plays a minor role at most in voters' decisions, and the electorate itself is not static. A great deal depends on which voters are excited enough to get to the polls and which voters are disengaged enough to stay home.

And in an era of partisan polarization, there are few voters in the middle left to persuade. In 2016 Hillary Clinton thought she could win over moderate Republicans who were disgusted with their party's nominee; she failed. In fact, if you look over recent presidential elections you’ll see one supposedly moderate candidate after another losing, while the winners are almost always those who excite their own party enough to drive turnout. In order to find a presidential nominee who lost because he was too far out of the ideological mainstream, you’d have to go back almost half a century to George McGovern in 1972. Meanwhile, the list of losers is heavy with candidates who thought they would win if only voters understood how moderate they were.

Nobody understands this better than Republicans, who manage to regularly win elections with a spectacularly unpopular policy agenda of tax cuts for the wealthy, outlawing abortion, taking health coverage from millions of people, and exacerbating climate change. If it was all about who could be more of a centrist, they’d never stand a chance.

Nobody understands this better than Republicans, who manage to regularly win elections with a spectacularly unpopular policy agenda of tax cuts for the wealthy, outlawing abortion, taking health coverage from millions of people, and exacerbating climate change. If it was all about who could be more of a centrist, they’d never stand a chance.

Then they get quoted in news stories explaining that rationale for their decision, and the cycle continues. As one voter told the Times’s Lisa Lerer, “I like Joe. We need someone in the first place who’s electable in 2020. Look, my own personal beliefs are probably a little to the left of where he is, but independents are going to be crucial in 2020.”

When voters put on their pundit hats in this way, they adopt the same fear and distrust of the electorate that characterizes so many elected Democrats—including, it appears, Nancy Pelosi. They think that if Democrats offer liberal policy ideas then the public will reject them, no matter how many polls they see showing that their policy agenda is vastly more popular than what Republicans favor.

They’ve bought into a conservative myth, one that has existed for some time. As multiple studies by political scientists have shown (see here or here), elected officials tend to believe their own constituents are more conservative than they actually are. Most remarkably, that’s true of both Republican and Democratic officeholders (though the Republicans overestimate the public's conservatism by wider margins).

Pelosi likes to point out that many of the Democrats who won in 2018 came from swing districts and stopped short of advocating single-payer health care or a government jobs guarantee, which is true. But it's also true that the Democrats won such big victories because turnout exploded—it topped 50 percent, compared to just 37 percent in the last midterm.

The 2020 election will be as complex as any other, but it isn't going to be determined by which candidate is closer to the ideological midpoint. If Democrats are going to win, they’re going to have to nominate someone who gets their own party’s voters motivated to organize and get to the polls. That could be any number of candidates, even Joe Biden. But it won't be because they took positions designed to offend as few Republicans as possible.