Read: Suburban-rural districts are turning on the GOP.

As Garin’s observation suggests, the danger to Republicans in the Clinton-won seats is a feature, not a bug, of Trump’s electoral approach. In terms of both policy and rhetoric, Trump has focused his presidency almost entirely on the priorities and peeves of his base. Trump demonstrated that instinct again this week by wrapping himself around the newly confirmed Supreme Court Justice Brett Kavanaugh and escalating his attacks on the women who accused the judge of sexual assault—even though national polls just before and after the Senate vote showed that most Americans believed the women and opposed Kavanaugh’s ascension.

Trump’s base-first approach to the presidency has produced some tangible political benefits for Republicans. It has strengthened them in most House districts outside of the major metropolitan areas. That’s also true in heavily rural and predominantly white heartland states, such as North Dakota, Montana, and Missouri, where Democrats are defending Senate seats next month. And, particularly in the aftermath of the Kavanaugh confrontation, his approach has given Republicans hope that they can minimize the usual falloff in midterm turnout for the party that holds the White House.

But the downside of this strategy—the trade-off Trump is imposing—is measured in the danger gathering for House Republicans in swing districts, primarily in white-collar suburbs, where the party can’t win just by increasing GOP turnout and instead must appeal to a broader range of voters. That risk extends beyond just the Clinton-Republican districts: Democrats are seriously contesting more than two dozen House seats that narrowly voted for Trump in 2016, though the increased GOP energy evident after Kavanaugh could push some of those seats out of reach. The epicenter, then, of the GOP’s House vulnerability remains the 25 Republican-held districts that rejected Trump for Clinton from the outset.

Today, political analysts of both parties describe only three of the Republicans in these seats as clear favorites: Representatives David Valadao in California’s Central Valley, Will Hurd in West Texas, and John Katko in upstate New York, none of whom represent suburban white-collar districts. Two other incumbents in urban areas hold more modest advantages: Carlos Curbelo in Miami and Brian Fitzpatrick outside Philadelphia.

But public and private polling suggest that nine of these seats—all of them centered in the suburbs—are already virtually lost causes for the GOP. That list starts with the incumbents Mike Coffman, near Denver; Erik Paulsen, near Minneapolis; Kevin Yoder, near Kansas City; and Barbara Comstock, in Northern Virginia (though some Republicans insist, against the public-polling evidence, that her campaign still has a pulse). Republicans have also largely written off open seats in Clinton-won districts near San Diego, Tucson, and Philadelphia, and in Pennsylvania’s Lehigh Valley.