Vice President Kamala Harris will hold a rally in Milwaukee on Tuesday night at the same basketball arena where former President Donald J. Trump accepted the Republican nomination just a month ago, at a time when his party believed he was coasting to victory against a hapless President Biden.
Ms. Harris’s choice of venue is the latest in a series of aggressive moves that seem designed to get under Mr. Trump’s notoriously thin skin.
Crowd size is one of the former president’s most reliable bugbears. Ever since 2016 — when his huge rallies seemed to foretell his unexpected victory against Hillary Clinton — Mr. Trump has been obsessed with how many people show up to hear him speak and how many come to hear his opponents.
If Ms. Harris is able to fill up Fiserv Forum’s roughly 18,000 seats, it could ignite another angry reaction from Mr. Trump. He has already falsely accused the Harris campaign of using artificial intelligence to generate fake images of her crowd at a rally in Detroit. And he has also claimed, again without evidence, that his rally in Washington on Jan. 6, 2021, drew more people than the Rev. Dr. Martin Luther King Jr.’s “I Have a Dream” speech — bringing more attention to his role in the assault on the Capitol that happened later that day.
Ms. Harris has reshaped the race since replacing Mr. Biden on top of the ticket last month, raising hundreds of millions of dollars, generating a wave of enthusiasm from rank-and-file Democrats and narrowing the gap or even taking the lead against Mr. Trump in many polls of battleground states, including Wisconsin.
“Donald Trump is perhaps the most thin-skinned person ever to run for president,” said Representative Brendan Boyle, a Democrat from Pennsylvania. “So he’s fairly easy to bait and knock off message.”
The Harris campaign declined to comment. The Trump campaign did not respond to requests for comment.
Some of the antagonism by Democrats has lacked subtlety.
On Sunday night, the eve of the Democratic convention in Chicago, operatives with the Democratic National Committee projected a series of insulting messages onto a condo-hotel skyscraper owned by Mr. Trump in downtown Chicago.
One of the messages read “Trump-Vance: ‘Weird as Hell,’” an echo of a popular Democratic attack on Mr. Trump and his running mate, Senator JD Vance of Ohio. Another said “Project 2025 HQ,” a reference to the right-wing playbook for remaking the federal government that Mr. Trump has tried to distance himself from.
And this month at a rally in Las Vegas, Ms. Harris called to eliminate federal taxes on tips for hospitality and service workers. Mr. Trump made a similar proposal at a rally in the city earlier in the summer.
The former president responded immediately and angrily to Ms. Harris’s proposal, writing on Truth Social that she had “copied” his own.
“This was a TRUMP idea,” he said. “She has no ideas, she can only steal them from me.”
Neil Vigdor contributed reporting.