For more than three years, Mr. MacArthur has largely made his name by fighting for the federal government to fulfill its responsibility to victims of Hurricane Sandy in 2012. That endeared him to constituents who are still struggling to rebuild their lives. Sandwiched between the Philadelphia suburbs and the retirement communities of the Jersey Shore, his district was hit hard by the storm, which left tens of thousands of buildings damaged or destroyed.
On Wednesday, though, protesters lined up for hours in the late afternoon sun to vent their frustrations with Mr. MacArthur. Some held signs that bore his likeness with the words “I took your health care” emblazoned on his forehead — right where Representative Nancy Pelosi of California, the Democratic leader, had warned Republicans their plan would be “tattooed.”
A hostile crowd assailed Mr. MacArthur, who by turns pleaded for respect and fell silent, a smile frozen on his face as attendees shouted over him. A man who identified himself as a resident of Fort Pleasant expressed concern about what would happen if he lost his job and Gov. Chris Christie opted out of the law’s protections.
“That’s a problem, and this is your amendment, sir,” the man said. “You brought it back from the dead. It’s yours. You own it.”
After a vow to take everyone’s questions, Mr. MacArthur’s town hall stretched on for more than four hours.
It was a sobering conclusion to a victory lap that started with backslaps in the White House Rose Garden shortly after the House’s 217-213 vote. As his fellow Republicans grinned and shook hands with a beaming President Trump, Mr. MacArthur quietly slipped in on stage left.
After half an hour of jubilant thank-you speeches, Mr. MacArthur recounted the profound effect of watching his father struggle to pay off his mother’s medical bills years after her death.
“I watched him all my life working three jobs to pay off medical bills because he had no insurance when my mother died of cancer when I was 4,” Mr. MacArthur said at the time. “He paid those bills off when I was in college.”
Mr. MacArthur reluctantly revealed in news media interviews another motivator behind his commitment to health care: the death, decades ago, of his 11-year-old daughter, who was born with a rare neurological disorder.
Their painful experience with the health care system gave Mr. MacArthur, who had a 28-year career in insurance, an appreciation for the struggles of other families.
“How do you negotiate with a hospital who just did surgery on your daughter, but you’re questioning how a two-hour surgery can cost 15 or 20 thousand dollars?” he said in an interview Wednesday. “I was in that boat.”
“That’s tough for him to bring up, but I think it’s necessary for him to do that,” said Mark Aussicker, a longtime colleague and friend who attended the funeral for Mr. MacArthur’s daughter. “He’s doing that just to help people understand he’s been there, too, to some degree.”
But his attempts to paint himself as a relatable, sympathetic figure have seemingly fallen flat. Even a longtime local newspaper columnist, Tom Moran, who once bonded with Mr. MacArthur over his own son’s death, savaged him for having made the bill “even more brutal.”
While Mr. Obama won Mr. MacArthur’s swing district twice, Mr. Trump carried it in 2016, making it no easy pickup as Democrats seek to take back the House. But the Republican health care plan has provided an opening for Democrats, who had little early success against Mr. MacArthur.
As soon as the details of Mr. MacArthur’s amendment emerged, the Democratic Congressional Campaign Committee released digital ads in 30 districts to “educate voters” — reserving a five-figure buy for Mr. MacArthur’s.
“He was already in a vulnerable position this cycle, and the fact that he was willing to rip away protections for people with pre-existing conditions is a game-changer for our ability to compete in this district,” said Meredith Kelly, the D.C.C.C. spokeswoman.
Mr. MacArthur’s decision to negotiate with the hard-right House Freedom Caucus, the other cluster of “no” votes on the first version of the Republican health care plan, irked many of his fellow moderates, many of whom worried that the final version lacked protections for Americans with pre-existing conditions. Representatives Frank A. LoBiondo, Leonard Lance and Christopher H. Smith, also of New Jersey, voted against it.
With Senate Republicans making no secret of their intention to rewrite the bill, the question is whether Mr. MacArthur traded his moderate credentials for doomed legislation.
“If they send back any bill at all,” Representative Charlie Dent, Republican of Pennsylvania said, “it will be in a form that will likely be rejected by those who were just appeased in the House in order to move the first bill.”
Mr. MacArthur is among a small group of Republicans holding town halls during this one-week recess. Some have already faced their own crowds and were often drowned out by boos as they tried to explain their stances.
As protesters waved a skeleton outside, Mr. MacArthur acknowledged that he was not expecting to change minds.
“I don’t think I’ll convince people necessarily, but they deserve to know where I’m coming from, they deserve to know how I think about things,” he said. “They deserve to be able to tell me what they think.”