Whether Mr. Biden can better navigate the debate stage and, perhaps, even score a few points of his own are the central questions. His last performance raised concerns not only about his preparation but also, as my colleagues reported today, about his age. Another lackluster showing could cost the former vice president his front-runner title.

“I’m not going to be as polite this time,” he told supporters at a fund-raiser last week.

Here are some other things I’ll be watching for:

Race takes center stage.

A discussion of race feels all but inevitable in the debates, given that they’re coming after a month of attacks by President Trump on prominent Democrats of color and will take place in a city that’s nearly 80 percent black.

It’s a conversation many on the stage want to have, both with the president and with each other. Mr. Biden and his top aides spent much of the past week sparring with Ms. Harris and Senator Cory Booker, two black candidates, over their civil rights and criminal justice records, and on Wednesday night he will be sandwiched between them.

They aren’t the only ones eager to talk about civil rights and criminal justice issues, either: Pete Buttigieg needs to win more support from voters of color, and Julián Castro, whose boffo performance in the first round of debates allowed him to hire some staff, has put reforming the criminal justice system at the center of his campaign.