How the Fight to Define Kamala Harris Will Shape Next Week’s Debate

The battle over who Ms. Harris is — and what she stands for — will take center stage on Tuesday when she and Donald Trump debate for the first time.

For eight years, Donald J. Trump has singularly dominated the American political landscape. But as he prepares to debate Vice President Kamala Harris for the first time next week, the former president is facing a rare moment when the spotlight will be far more on his opponent than on him.

The race to define Ms. Harris has emerged as a central political battleground of the 2024 contest since her surprise entry replacing President Biden in July.

Voter sentiments about Mr. Trump have hardened after a decade in the public eye. Those sentiments have been effectively frozen even after impeachments, indictments, a felony conviction and an assassination attempt. In comparison, Ms. Harris’s support has been volatile. Voter views of the vice president have improved suddenly and sharply in the nearly seven weeks of her candidacy, strengthening her standing against Mr. Trump.

For Ms. Harris, the debate on Tuesday is her best chance to solidify those gains. For Mr. Trump, it is his greatest opportunity to undercut or reverse them.

The event will be Mr. Trump’s seventh time taking the stage in a general-election presidential debate — the most of any candidate in the modern era — while it will be Ms. Harris’s debut. Strategists allied with each campaign said that means there is little new information to be gleaned about him and much for voters to learn about her.

“Voters decided on Donald Trump in 2016 and have not changed their mind,” said Robert Blizzard, a veteran Republican pollster. “The difference is voters have started to change their minds on Kamala Harris.”