At his numerous campaign rallies, President Trump frames the November midterm election in sweeping terms. The Democrats, he has said, want to erase the country’s borders and allow crime to flourish. If they take power, the country will “plunge … into gridlock, poverty and chaos.”

What’s more, he claimed on Twitter last week, the fight over Brett M. Kavanaugh’s nomination to the Supreme Court was “having an incredible upward impact on voters.” Republicans not motivated by concerns about the apocalypse that would result from Democrats having slight majorities on Capitol Hill were instead motivated by the Democrats' efforts to block Kavanaugh’s confirmation.

Unsubtly, Trump hopes to position the upcoming election on turf that's favorable to his party. By trying to make the election about immigration and crime, he and his allies think, they have an advantage. By suggesting that Democrats will harm the economy, by arguing that they are simply partisan obstructionists, Trump hopes to spur Republicans to prioritize voting next month.

But in an op-ed that ran in USA Today on Wednesday, Trump let the mask slip. In about 800 words, he argues against a very specific policy proposal that some Democrats embrace: expanding Medicare to cover all Americans. Littered with similarly hyperbolic language used at his campaign rallies (“The new Democrats are radical socialists who want to model America’s economy after Venezuela."), Trump’s essay is nonetheless centered not on crime or Kavanaugh but on health care.

Of course it is. Health care has consistently been at the center of the 2018 campaign. Analysis of ads run by federal candidates shows that more than 40 percent of spots mentioned the subject last month, up from less than a third in the first half of the year.

(Philip Bump/The Washington Post)

Despite Trump's constant mentions of borders, ads supporting Republicans mentioned immigration less last month than at any point this year. A campaign rally speech is one thing. An investment of tens of thousands of dollars in a TV ad is something else.

About half of ads supporting Democrats have mentioned health care over the course of 2018. Likely in part as a response, ads backing Republicans are increasingly mentioning health care as well, with the subject about as common now as taxes.

In part that’s because Republican candidates are trying (as Trump did) to use support for “Medicare-for-all” against their opponents. The Washington Post’s fact-checkers noted a number of recent instances in which Republicans alleged that the Democrats they’re facing support a single-payer health-care system even when the Democrats don’t actually hold that position.

Why do that? We noted in September that the Democrats have a consistent advantage on health care as an issue in the abstract. The Affordable Care Act (Obamacare) is now viewed positively on net, and voters trust the Democratic Party on health care by double-digits over Republicans in polling.

(Philip Bump/The Washington Post)

So Trump and his party are trying to use that strength against them, extending a subset of the Democratic message into friendlier turf: Medicare-for-all would put seniors at risk and would push the nation into socialism. On Twitter, The Post’s Glenn Kessler walked through ways that Trump’s rhetoric in USA Today was misleading or false, but the intent of the piece isn’t the details, it’s the rhetoric.

There’s increasing evidence that the political fight over Kavanaugh may not be a big long-term boost to Republicans. A CNN poll this week showed that views of Kavanaugh were more broadly negative among the most enthusiastic voters than the population overall, not what you’d expect to see if Trump’s tweet had been accurate. A Pew Research Center poll released late last month found that the Supreme Court was cited as the most important midterm issue — but that more Democrats than Republicans held that position. Google search traffic for information about the Supreme Court fight surged when Kavanaugh was testifying, but in most states has now faded.

Health care, on the other hand, is consistently the most searched political topic. It was also the second-most important issue cited in Pew’s September poll.

The midterm election is shaping up to be good for the Democratic Party, at least in the House. That health care is at the center of the campaign isn’t the only or even the primary reason. (The primary reason is Trump.) But for all of Trump’s rhetoric about what’s really at stake next month, his essay Wednesday makes clear that he and his party are fighting these races on the unfriendly policy terrain of health care — and that they know it.