The campaigns of Stacey Abrams in Georgia, Andrew Gillum in Florida and Beto O’Rourke in Texas may have electrified black and progressive white voters — just as Ms. Hyde-Smith’s comments may energize Mississippians to support Mr. Espy — but they had an equal and opposite effect as well: in rural county after rural county, this trio of next-generation Democrats performed worse than President Barack Obama did in 2012.

As Jackson Mayor Chokwe Lumumba put it, Ms. Hyde-Smith’s comments are “going to excite two different demographics: the base of supporters that follow this Trump ideology of saying what you want, and those individuals who share a close connection to that dehumanizing history.”

More ominous for Democrats was that the deep losses this year among rural and some exurban whites were not just confined to Southern states where they nominated unabashed progressives with hopes of transforming the midterm electorate. They lost four Senate seats, as well as governor’s races in states like Iowa and Ohio, with more conventional candidates whose strength in cities and upper-income suburbs was not enough to overcome their deficits in less densely populated areas.