Mr. Trump now leads Mr. Biden 49 percent to 43 percent among likely voters nationally, a three-point swing toward the Republican from just a week earlier, before the debate. It is the largest lead Mr. Trump has recorded in a Times/Siena poll since 2015. Mr. Trump leads by even more among registered voters, 49 percent to 41 percent. ...

Overall, 74 percent of voters view him as too old for the job, up five percentage points since the debate. Concerns about Mr. Biden’s age have spiked eight percentage points among Democrats in the week since the debate, to 59 percent. The share of independent voters who said they felt that way rose to 79 percent, nearly matching the Republican view of the president.