“Has anybody come to talk about the farm bill?” Mr. Grassley asked hopefully, looking up from the list in his hands.

They had not.

Instead, for the next hour, Mr. Grassley was bombarded with complaints about Mr. Trump’s tariffs, anger about his actions on immigration, grievances over his efforts to take an ax to the federal government and frustration that the Republican-led Congress had done little to rein him in.

“We would like to know what you, as the people, the Congress who are supposed to rein in this dictator — what are you going to do about it?” one man asked, gesticulating as much of the crowd applauded. After criticizing the Trump administration’s deportations, the man scowled, leaned toward Mr. Grassley and asked, “Why won’t you do your job, Senator?”

The senator opened his mouth, but his tentative reply was drowned out by others echoing their disapproval.

With Congress in a two-week spring recess, Mr. Grassley was among the few Republican members of Congress who dared to hold such a freewheeling gathering with constituents, amid an increasingly vocal backlash to Mr. Trump. Those who are holding town halls have embraced strategies meant to limit the possibility of volatile confrontations or embarrassing social media video of rooms full of hecklers.

Some Republicans, like Representatives Tim Burchett of Tennessee and Nancy Mace of South Carolina, turned to virtual formats, such as telephonic town halls with screened questions, that effectively shielded them from spontaneous in-person interactions. To attend a meeting with Representative Brian Mast of Florida, audience members had to prove that they lived in the district before walking through the door.

Representative Marjorie Taylor Greene of Georgia, who also made constituents preregister and prove residency, answered only pre-submitted questions rather than hand attendees at her town hall this week an open microphone and the opportunity to rail at her.

Representative Marjorie Taylor Greene’s town hall in Acworth, Ga., devolved into chaos on Tuesday as police officers forcibly removed two people who heckled her.Credit…Nicole Craine for The New York Times

None of it succeeded in tamping down the palpable anger and anxiety that dominated the sessions. Mr. Grassley on Tuesday frequently strained to be heard over a jeering crowd that shouted him down, called his answers insufficient and accused him of abdicating his responsibilities to keep the administration in check.

Though Mr. Grassley’s list of issues seemed tailored to steer the town hall away from hot-button topics and toward calmer fare, nearly every topic turned into a referendum on Mr. Trump, and almost every question asked was critical of the administration.

In the event’s most contentious exchange, Mr. Grassley was asked by a man who described himself as “pissed” whether he would do anything to help secure the return of Kilmar Armando Abrego Garcia, the Salvadoran immigrant residing in Maryland who was deported last month in what the Trump administration has acknowledged was a mistake, and incarcerated in a notorious prison in El Salvador.

When the senator twice said Mr. Abrego Garcia’s fate was out of his hands, he was met with resounding groans and boos.

In spite of the entry requirements and heavy police presence at Ms. Greene’s town hall in Acworth, Ga., it devolved into chaos almost immediately, as two men who heckled her were forcibly removed after the police used a stun gun on them.

Ms. Greene seemed to relish the confrontation. Even before her event began, she said that she was looking forward to “throwing out” anyone who caused a scene.

“I’m not backing down, and I don’t think my colleagues should, either,” she said in an interview. “Whether people vote for us or not, we serve our district.”

Still, Ms. Greene was an exception. After a number of Republican town halls over the past two months prompted embarrassing confrontations that circulated widely online, party leaders suggested that representatives avoid in-person events and the risk of any further clashes. Many were all too happy to heed the call.

Some in the crowd at Ms. Greene’s town hall shouted in support of the removal of protesters. Credit…Nicole Craine for The New York Times

Democrats have largely continued to hold town halls, with some of them working to fill the void left by their Republican colleagues by traveling to their districts to show that their party is more responsive to voters’ concerns.

Representative Sean Casten, Democrat of Illinois, drove hours outside his suburban Chicago district over the weekend to small towns in the middle and south of the state, whose local Republican representatives, Darin LaHood and Mike Bost, have so far declined to hold in-person town hall meetings.

“Our congressman is absent without leave,” said one man in Mr. Bost’s district who told Mr. Casten he was concerned about his mother’s access to Social Security and Medicare benefits. “We don’t get to talk to him.”

And even as Mr. Grassley’s constituents in Iowa grilled him on his support of Mr. Trump’s policies and his votes on recent bills, many of them said they still appreciated the senator’s coming to face them.

“Thank you for coming today,” Cindy Steflik, a retiree from West Point, Iowa, said before sharply questioning Mr. Grassley about cuts to the Department of Veterans Affairs. She added that she believed the area’s Republican representative, Mariannette Miller-Meeks, “seems to be hiding in a closet.”

Anthony Cruz, a spokesman for Ms. Miller-Meeks, said that she held a telephone town hall earlier this year with 12,000 Iowans and that she planned to hold town halls in her district in the future.

Security outside Mr. Grassley’s town hall on Tuesday.Credit…Thalassa Raasch for The New York Times

An attendee, Cindy Steflike, at Mr. Grassley’s town hall.Credit…Thalassa Raasch for The New York Times

At times, when the soft-spoken Mr. Grassley, currently serving his eighth term in the Senate, was being drowned out by angry constituents, others would jump in, urging fellow attendees to let him finish. Still, Mr. Grassley often struggled to control a combative room. He at times stammered through defenses. More often, he simply stood still, his face blank as he waited for the crowd to finish venting its dissatisfaction with him before trying to answer a question.

Afterward, Ms. Steflik said that she was “disappointed” with Mr. Grassley’s responses, accusing him of sidestepping thorny issues.

“He doesn’t respond to everything,” Ms. Steflik said. “It’s usually just kind of a circling around the corral.”

Mr. Mast, who also faced boos and jeers at his town halls, was more combative in response, doubling down on his support for the president and his administration.

“There won’t be any cuts to Social Security,” Mr. Mast declared in response to a question at his town hall in Palm City, Fla., on Tuesday afternoon.

“Liar!” a member of the crowd yelled as others booed.

Ms. Greene spoke to journalists after her town hall this week.Credit…Nicole Craine for The New York Times

Ms. Greene, a firebrand MAGA star who delights in mocking liberals, made a show of fielding hostile questions from the batch she read aloud, using them as prompts to ridicule critics of her and Mr. Trump.

“Why is M.T.G. supporting Musk and DOGE and the slashing of Medicaid, Social Security offices, libraries and more?” she read, quoting a question about the Department of Government Efficiency from a person identified only as Sarah. “This is outrageous.”

Ms. Greene smiled wryly and, as though she were gently scolding a small child, sardonically replied: “Well, Sarah, unfortunately, you’re being brainwashed by the news that you’re watching.” The crowd cheered and whooped its approval.

Eric Nord, a Republican from Acworth who was added to Ms. Greene’s district two years ago when maps were redrawn from redistricting, said he was disappointed by the event. He wanted to hear from Ms. Greene about how she was prioritizing local issues and to gain some insight into how she might court voters in this more moderate corner of her district.

Instead, he said, the town hall felt more like a political rally than a true forum for constituents to air their concerns to a receptive representative.

“It’s just such a shame that people can’t voice their opinion without completely taking over an event,” Mr. Nord said, speaking both of the hecklers in the room and Ms. Greene’s aggressive tactics to remove them. “It’s just a disappointment that you can’t really have a discussion.”