Protesters stormed the office of a former senator, demanding that she leave. She refused.

Former Senator Heidi Heitkamp sat in her second-floor office at the University of Chicago’s Institute of Politics, preparing for appeared on a television news program Friday afternoon, when three pro-Palestinian protesters wearing masks and sunglasses stormed in and ordered her to leave the building.

Ms. Heitkamp, ​​the institute’s director and the only staff member left in the building, refused to leave, delaying an attempt to take over the building. It was the latest tactic in the demonstrations over the war between Israel and Hamas that have taken place on the University of Chicago campus and across the country.

“They were desperate to get me out,” Mrs. Heitkamp recalled. “I told them, ‘I’m not leaving. This is our building.’ And I planted my feet. She added: “I’m a stubborn old woman.”

Ms. Heitkamp, ​​who represents North Dakota as a Democrat in the Senate, said she tried to engage in dialogue with the protesters about their goals and why they targeted the institution, even as she heard others in other rooms destroying furniture.

“I was trying to find common ground,” she said. “They kept saying, ‘Aren’t you worried about your safety?’”

The confrontation ended, she said, when campus police officers suddenly arrived and some protesters, who had brought an extended supply of bagels and water, fled out the windows.

In a statement Friday, the protest group said it occupied the building to protest the University of Chicago’s ties to Israel. Bystander video showed protesters climbing through second-floor windows to exit the building as the crowd below cheered.

After the demonstrators were cleared from the building, other demonstrators remained outside, chanting, shouting and beating drums. They were about two blocks from where police had removed a protest camp last week,

Jeremy Manier, a university spokesman, said in a statement that protesters had tried to block the entrance to the building, damaged property and ignored law enforcement orders to leave.

Earlier in the day, the institute held a board meeting in the building that included David Axelrod, the organization’s founder and a senior adviser to President Barack Obama.

Mr. Axelrod and Ms. Heitkamp issued a statement later in the day: “We recognize protest as a time-honored part of the democratic process. But the occupation of buildings, the destruction of property and the infringement of the rights of others are not.”

Ms. Heitkamp said she never felt threatened by the protesters who showed up at her office, nor did she feel like she was being held hostage. “They knew who I was — they called me senator,” she said. “They just wanted me to go away.”

“I tried to explain that we at the IOP are a place of dialogue,” she said.

“We are neutral,” she said, adding: “Our role at the university is to really create a space for dialogue.”

The Institute of Politics is two doors down from the University of Chicago Hillel and across the street from Rohr Chabad, where some students were having a Shabbat dinner when the demonstration began. As the protest continued, counter-protesters held Israeli flags in view of the pro-Palestinian demonstrators. Rock music came from a nearby house in what appeared to be an attempt to drown out the protest chants.

A sign identifying the Institute of Politics building was covered with a cardboard sign that read “permanent cease-fire now” and a number of demands were posted on the building. One of the demands was “abolish the university.”

A group of protesters from the University of Pennsylvania also tried to occupy a campus building on Friday evening. University police and Philadelphia police made several arrests and evacuated the building, Fisher-Bennett Hall. The hall is located across the street from College Green, the site of the encampment that was cleared by police last week.

Mattathias Schwartz, Bob Chiarito, Jeremy W. Peters and Natalie Pompilio contributed reporting.