“Once low-income people are receiving good health care for the first time, it becomes very difficult for a member of Congress to take that assistance away from them,” said Senator Susan Collins, Republican of Maine. “To deprive them of that health care is something that now makes a lot of people in my party uncomfortable.” She has co-sponsored a replacement plan that would let states keep many of the law’s components now under fire from House Republicans.
President Trump has heightened the stakes, at times insisting that lawmakers replace the law immediately while repeatedly saying that no one should lose insurance coverage under a replacement plan. Patients with chronic illnesses, drug addicts, rural hospital executives and expectant mothers — many of whom voted for Mr. Trump — have made it clear that they will not support any plan that deprives them of what they now have, even if they dislike its origins in the Obama administration.
“Voters may not know how they got their health care,” said Senator Joe Manchin III, Democrat of West Virginia, who has long endorsed making changes to the law, “but they sure will know who took it away.”
Republicans hope to send a new health care measure to the president’s desk this spring, but vast chasms have been exposed between the most conservative members and other Republicans, and the White House has yet to provide clear guidance by endorsing specific provisions.
While promising to maintain the most attractive parts of the law, like forcing insurers to offer coverage for patients with pre-existing conditions, congressional Republicans have long set a central goal of ensuring “access” to care — not guaranteeing care — while shoring up the insurance marketplace.
But Mr. Trump upended that message when he said in January that any Republican plan would “have insurance for everybody,” a notion he has repeated. Lawmakers have taken notice, sometimes echoing his language.
“I think the no-gaps-in-coverage part is important,” Ms. Capito said, noting that expanded coverage was the Obama administration’s main focus. “For every push, there is a pull.”
Mr. Trump has further complicated matters by insisting that any plan replace the law as soon as it is repealed; Republicans had hoped to put the replacement off.
In addition, the Affordable Care Act’s Medicaid expansion — which has extended coverage to roughly half of the 20 million people who have gained insurance under the law — has been embraced by a majority of governors. Many of them, including Republicans, have said in meetings with both lawmakers and Mr. Trump that they want to continue that program.
“While I clearly have concerns about the expansion’s long-term costs,” Senator Lisa Murkowski, Republican of Alaska, said in an address to the State Legislature last month, “it has strengthened our Native health system and reduced the number of uninsured that are coming into our emergency rooms.
“So as long as this Legislature wants to keep the expansion,” she continued, “Alaska should have the option. So I will not vote to repeal it.”
Even senators in states with no Medicaid expansion concede that the law is baked into the culture, sometimes in ways their constituents are not fully aware of, and in ways they themselves have fought for. Most notably, the Affordable Care Act has increased money and access to programs for Americans with mental illness and drug addiction, especially in states, like Ohio, that accepted the Medicaid expansion and have a large population of opioid drug abusers.
“While we work to reform Medicaid as part of replacing the A.C.A.,” said Senator Rob Portman, Republican of Ohio, who has made the opioid crisis one of his chief concerns, “close attention must be paid to the growing opioid epidemic and the need for drug treatment and recovery.”
Many states that overwhelmingly supported Mr. Trump’s presidential campaign are some of the biggest beneficiaries of the health care law, even if their governors chose not to accept the Medicaid expansion. In some cases, those states still found ways to use the law to offer services like cancer screenings. Other, less-celebrated programs have been a boon, like one that permitted states to create medical “homes” for patients with multiple chronic conditions.
“One of the things that is underappreciated is that there are lots of little things in the A.C.A. that a bunch of red states took advantage of, even if they didn’t expand,” said Richard Frank, a Harvard Medical School professor who worked at the Department of Health and Human Services in the Obama administration. He cited programs for disabled people in Louisiana and Missouri, and guidelines that allowed states to redefine poverty lines to get more residents covered by Medicaid even without the federal expansion.
“Those turned out to be very useful for their costly populations,” Dr. Frank said. “It’s unclear, if they repeal, if Congress would take those away.”
As residents become aware that benefits they have received were part of the health law and may go away, so do their elected representatives.
“In some ways it has been a health care education process for everyone,” Mr. Manchin said. “Even for people here.”