In the 2024 presidential election, Karl Lenker is voting for former President Donald J. Trump. His girlfriend of a decade, Jan Lewin, is voting for Vice President Kamala Harris.

So Ms. Lewin, 67, did not appreciate the Biden-Harris “Dumb and Dumber” mug that her partner bought for his morning coffee. Nor was she a fan of the toilet paper featuring President Biden’s face that he put in the bathroom of their condo in Atlanta. (Ms. Lewin retaliated by swapping it out for Trump-themed toilet paper.)

Mr. Lenker, 74, a self-described “libertarian Republican,” does not hold back when it comes to talking politics. He believes Ms. Harris is a puppet being used to push a “liberal left” agenda that he calls “insane.”

“Not all Democrats are stupid,” Mr. Lenker said. “But all stupid people vote Democrat.”

Ms. Lewin tries not to be baited by Mr. Lenker’s ribbing, but she can be equally blunt: “I try not to attack Trump unless he’s doing something so stupid I can’t help it,” she said.

Mr. Lenker and Ms. Lewin aren’t the only couple sparring over political ideology in the run-up to this historically tight presidential election. Recent estimates say about one-third of couples do not share a political affiliation, and for true split-ticket couples (6 percent or fewer marriages are between a Democrat and a Republican) this may be a “precarious moment,” said Cynthia Peacock, an associate professor of communication studies at the University of Alabama who researches politically mismatched relationships.

Ms. Peacock’s research has found that people in such relationships tend to report slightly lower levels of relationship satisfaction than those who share the same views as their partner. “Political attitudes, you know, they’re not just like the opinions we have about our favorite movies or foods,” she said. “They’re tied to our morals, to our identity, to things we hold very deeply and personally.”