Could an old-school approach to voting decide the midterms?

Election Day is here, and voters will reveal whether tightening polls in competitive statewide races will mean a “red wave” sweeps the country.

If that wave turns out not to be as strong as expected, Democrats can likely thank split-ticket voting, the practice of electing candidates from different political parties for different statewide, congressional, or presidential races.

Split-ticket voting was once far more common, in part because of a belief expressed by Elon Musk recently. In endorsing Republicans up and down the ballot Monday night, he argued that “shared power curbs the worst excesses...