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The police in Burlington, Vt., warned that Donald J. Trump’s campaign has confirmed that 6,500 people plan to attend a rally on Thursday in an arena that seats only about 1,400.

For Mr. Trump to schedule a visit to the hometown of Senator Bernie Sanders, whom he regularly tweaks as a “socialist-communist” or even a “maniac,” is certainly a provocation. For the Trump campaign to plan on a large overflow, leaving many people in the street, where the police expect counterprotests, seems to be kicking it up a notch.

“The Burlington Police Department, and the city generally, welcomes everyone who wishes to take part in the democratic process,” the police said in a statement released on Wednesday, adding that “there will likely be protests, demonstrations and rallies from different political perspectives in the city’s public spaces.”

The Trump rally is scheduled for the Flynn Center for the Performing Arts at 7 p.m.

Noting that event planners often distribute more tickets than seats for political rallies, anticipating no-shows, the police said that the Trump campaign reported issuing 20,000 free tickets, of which “at least 6,500” people have confirmed. The department warned of potential traffic congestion and urged people to arrive by “public transportation, foot or bicycle.”

Mr. Sanders’s political ascent began with his election in 1981 as the mayor of Burlington, which became known as the “People’s Republic of Burlington” for its leftist culture. It would seem hostile ground for Mr. Trump, although he has a lead over other Republicans in Vermont polls.

At the rallies of both candidates, many attendees express overlapping concerns on issues — opposing trade deals that eliminate manufacturing jobs, cuts to Social Security, wealth inequality and the hollowing out of the middle class.

Mr. Sanders welcomed Mr. Trump to Burlington in a statement.

“I hope his presence here will help him better understand Vermont values — social and economic justice, tolerance, respect for all people and the environment,” he said.