Mr. Trump’s convincing sweep of the primaries in Connecticut, Delaware, Maryland, Pennsylvania and Rhode Island on Tuesday did little to assuage concerns about his standing with swing voters in November. His victory speech included a bracing broadside against Hillary Clinton’s playing the “woman card.” And he continues to trail his opponents, Senator Ted Cruz of Texas and Gov. John Kasich of Ohio, among Republican women.

But ticket-splitting voters in federal races have become increasingly rare over the last two decades, hitting a low in 2012, when only 10 percent of them divided their votes between parties. That was down sharply from 1972. The ranks of straight-ticket voters have expanded along with the rise in partisanship and its attendant rancor in Congress.

“There is no doubt that, over all, the era of polarization and hyper-partisanship above and beyond idiosyncratic factors — that has to lead to a drop in ticket splitting,” said Richard Born, a professor of political science at Vassar College and an expert on congressional elections.

“Democrats and Republicans alike, as part of the polarization phenomenon, are more consistently liberal or conservative across issues,” Mr. Born said, “as are the candidates themselves, meaning less likelihood of ticket splitting.”