Former President Donald J. Trump and Vice President Kamala Harris enter the homestretch of the campaign in a tight race, and with their only scheduled debate looming on Tuesday, Ms. Harris faces a sizable share of voters who still say they need to know more about her.

A national poll of likely voters by The New York Times and Siena College found Mr. Trump leading Ms. Harris, 48 percent to 47 percent, within the poll’s three-percentage-point margin of error and largely unchanged from a Times/Siena poll taken in late July just after President Biden dropped his re-election bid. Mr. Trump may have had a rough month following the president’s departure and amid the burst of excitement that Ms. Harris brought Democrats, but the poll suggests his support remains remarkably resilient.