Democrats have hoped that President Trump’s deep unpopularity would propel them to gains in next year’s midterm election as they fight to take control of the House and improve their position in the Senate.
But last year’s contests and this year’s special elections suggest a complication: Trump is so distinctive a politician that it’s hard to persuade voters that other Republican candidates are carbon copies of the president. Trump’s outsized persona makes even those Republicans who share his views seem more moderate, an important attribute to swing voters.
That presents a problem for the party out of power.
Midterm elections traditionally serve as referendums on the...