President Trump, 77, says he supports mental competency tests for holding political office although he doubts the constitutionality of requiring them. Expect the topic to gain traction as partisans highlight his and Mr. Biden’s stumbles as evidence that they’re not up to serving as commander-in-chief.

On Sunday, Mr. Trump told the host of “Meet the Press,” Kristen Welker, that he “aced” questions administered at Walter Reed National Military Medical Center in 2020. “I got everything right,” he said. “I’m all for the tests.”