If Democrats make big gains in the midterm elections in four weeks, it may not only be because their most loyal voters come out in force, or because their candidates have converted Republican voters to their cause. Instead, the Democrats’ dream blue wave could come from Republicans who sour on President Trump and stay home. It already has a name: the red undertow.

Across the country, signs are emerging of an enthusiasm gap between Democrats and Republicans, even among those who consider themselves likely to vote. A stretch of rural southwest Michigan — long a Republican stronghold — illustrates the point, with more signs for blueberries and eggs than for political candidates. Volunteers are not showing up to door-knock. And many voters say they are tuning this election out. “People are just more focused on everyday life,” said Lindsay Kronemeyer, 35, a conservative Christian mother of two who works in the construction industry. “I don’t hear the chatter on the Republican side of ‘Trump this, Trump that.’ He’s just not there in my head anymore.”