President Trump spouts some wacky ideas that are easy to dismiss, such as his bogus claim that mail voting leads to widespread fraud. But some of his thinking is spot-on, even if it’s diabolical.

Trump has one solid reason for wanting to curtail mail voting: Democrats are far more likely to vote by mail than Republicans. “That’s why you’re seeing the president trying to put a roadblock in front of the mail,” Lee Miringoff, polling director at Marist College, says in the latest episode of the Yahoo Finance Electionomics podcast. “If you’re a strategist, it’s huge.”

In the latest Marist poll, 62% of Biden backers said they plan to vote by mail, while 36% plan to vote in person. Among Trump backers, just 24% plan to vote by mail, while 72% plan to show up at a polling place on Election Day. That’s a giant gap that, in theory, would hurt Democrats if the US Postal Service was unable to deliver some ballots. If 10% of mailed-in ballots got lost or arrived too late to be counted, for instance, it would eliminate 6.2% of the Democratic vote but just 2.4% of the Republican vote. That could easily be decisive in swing states where turnout is crucial and the winning margin could be just a percentage point or two.

[Check out other episodes of the Electionomics podcast.]

The prospect of a surge in mail-in voting, amid the coronavirus pandemic, has led to an unlikely uproar at the USPS, where the new postmaster general, appointed by Trump, has started making changes that could interfere with voting in the fall. The postmaster, Louis DeJoy, now says he’ll postpone any changes until after the election. But Democrats remain outraged and will attempt to pass legislation in Congress to prevent any action at the postal service that could delay or invalidate mail-in ballots.

Republicans vs. Democrats and in-person voting

Republicans might be more reluctant to vote by mail because they believe Trump’s unsubstantiated claims about the higher likelihood of fraud. But demographic factors probably explain most of the difference between Rs and Ds. Republicans tend to be older, and perhaps more inclined to vote in person simply out of habit. Young voters are more likely to be Democrats, with many away at college on Election Day. The Democratic Party has also pushed its members to vote by mail more aggressively than the GOP.

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Trump has said openly that he fears a surge in mail voting because he thinks it would hurt Republican electoral odds. In March, Trump said if voting were easier, thanks to mail ballots and other steps, “if you’d ever agreed to it, you’d never have a Republican elected in this country again.” That’s debatable: Utah relies heavily on mail-in voting, and it’s a reliable red state.