As Debate Looms, Trump Is Now the One Facing Questions About Age and Capacity

The last time the nation held a debate with the presidency on the line, a candidate with about eight decades of life behind him faced the challenge of proving that he was still up to the job of running the country. He failed.

Two and a half months later, the cast of characters has shifted and another candidate heading toward the octogenarian club confronts his own test to demonstrate that he has not diminished with age. Whether he passes that test may influence who will be the next occupant of the Oval Office.

At 78, former President Donald J. Trump exhibits more energy and speaks with more volume than President Biden does at 81, but he, too, has mixed up names, confused facts and stumbled over his points. Mr. Trump’s rambling speeches, sometimes incoherent statements and extreme outbursts have raised questions about his own cognitive health and, according to polls, stimulated doubts among a majority of voters.

With Mr. Biden now out of the race, the politics of age have been turned on their head. Mr. Trump is now the oldest person ever to run for president on a major party ticket and, if he wins, would become the oldest president in history by the end of his term, when he would be 82. While he managed to sidestep questions about his own capacity while Mr. Biden was his opponent, the rival he will square off against at Tuesday’s prime-time debate in Philadelphia will be Vice President Kamala Harris, who at 59 is nearly two decades younger.

The issue has been propelled back into the campaign by some of Mr. Trump’s recent public performances, most notably a meandering, hard-to-follow answer to a question on child care at the Economic Club of New York last week. Asked how he would help American working families stressed by the