Who Might Replace Biden on the Top of the Ticket?

President Biden’s poor performance in the debate against former President Donald J. Trump has prompted widespread panic and pessimism within the Democratic primary over Mr. Biden’s status as their presumptive nominee. As the president is said to be weighing his political future, some Democrats are raising the possibility of nominating an alternative candidate and considering a roster of names.

At the top the list is Vice President Kamala Harris, whose status as Mr. Biden’s running mate makes her an easy candidate for the party to turn to as an obvious successor. But a crop of Democratic governors and other figures are often mentioned as well.

A candidate switch would most likely require Mr. Biden to agree to step aside. The risks of him doing so are real. Some of the highest-profile figures listed below have never endured the vetting and road test of a presidential race. There is a long list of candidates who looked great on paper and withered on the campaign trail.

“It’s not as easy as it sounds,” said Barbara Boxer, the former senator from California. “Being vetted for president is like no other vetting. We don’t know how these people would do.”

Here are a few of the contenders being discussed:

Credit…Doug Mills/The New York Times

Kamala Harris

Vice President Harris, a former prosecutor and senator of California, has at times struggled to define her role at Mr. Biden’s side. Initially charged with addressing polarizing and intractable issues like illegal migration and voting rights, she has been viewed by Democratic donors and supporters of Mr. Biden as a potential political liability. Though those concerns have eased, she has been weighed down by low approval ratings that are barely higher than the president’s.