The patient, at a tiny family planning clinic on the rural coast of Maine, had a history of cancer. Now she feared it might be back.

The clinic’s nurse practitioner, Vanessa Shields-Haas, performed a biopsy and confirmed the cancer’s return. The finding allowed the patient to see a specialist in Portland a week later, instead of waiting months.

“This is lifesaving care,” said Ms. Shields-Haas, who works at Maine Family Planning, a network of 19 clinics scattered across the state.

Clinics like these are an essential part of Maine’s health care system, especially in isolated regions that struggle with shortages of primary care providers. But because abortion is among the services it offers, Maine Family Planning is a target of a new Republican offensive aimed at blue states that still allow broad abortion access.

In July, the Trump administration cut off Medicaid payments to reproductive health care clinics that offer abortions and receive more than $800,000 per year in Medicaid funding. The move was seen as directed at Planned Parenthood, the nation’s largest provider of reproductive care and a longtime target of Republicans. But two smaller providers, Maine Family Planning and Health Imperatives, a network of seven clinics in southeastern Massachusetts, were also swept up in the measure.

The fallout will soon be felt by thousands of patients across the country, particularly in rural areas where there are few options. For many who first sought out Maine Family Planning because they needed birth control, gynecological exams or testing for sexually transmitted infections, the clinics have become trusted sources of other basic care, including routine physicals and management of diabetes and asthma.

Unable to continue absorbing the cost of the lost payments — about $165,000 per month — and unsuccessful in a legal challenge of the funding freeze, Maine Family Planning will stop delivering primary care on Oct. 31. It remains to be seen if cuts to more services, or clinic closures, will follow.

While the Trump administration limited the funding shut-off to one year for now, the affected clinics believe it is likely to become permanent without court intervention. The Maine clinics serve 10,000 patients directly, and 20,000 more at dozens of other family planning sites that they help fund and oversee. Of the 30,000, about 70 percent qualify for free or reduced-cost care based on low income, and half get their health care through Medicaid.

“People are going to have to travel longer distances, or they’re going to go without care,” said Olivia Pennington, director of advocacy for Maine Family Planning. “We are a cornerstone of Maine’s health care system, and forcing us into this position puts even greater strain on that system.”

It is already illegal for federal funding to pay for abortion in most cases, and no Medicaid funds had been used to cover the procedure at Maine Family Planning, Ms. Pennington said. Instead, it covers other care that the clinics provide to their many Medicaid patients.

The organization offers surgical abortions at one clinic, in Augusta, and medication abortions at its other sites. Of about 700 abortions provided last year, 80 percent were via medication.

Planned Parenthood had initially been protected from the loss of funding, after a judge issued an injunction in its favor in July. But a federal appeals court overturned that ruling last month. In a statement, Planned Parenthood said the “catastrophic” cuts would place 200 of its 600 clinics around the country at risk of closing. It has vowed to continue providing abortions.

Clinics in red states are feeling the cuts, too. Planned Parenthood this week closed its two remaining clinics in Louisiana, where abortion is banned in almost all circumstances, and two others in Ohio in August.

Along with Maine and Massachusetts, California, Hawaii, Oregon and Washington are among the Democratic-led states scrambling to make up for the loss of federal funds. In Washington, Gov. Bob Ferguson, a Democrat, has pledged $11 million to cover the lost Medicaid funding for Planned Parenthood. But the State Legislature faces a multibillion-dollar gap between expected revenue and expenses over the next four years.

Advocates said that cuts to another key funding source for clinics that serve low-income Americans, a federal family planning program known as Title X, could come at any time.

“We aren’t going to see federal attacks lessen,” said Gabbi Nazari, government relations director for Pro-Choice Washington, an abortion rights group. “We’re going to see them intensify.”

In Maine, Gov. Janet Mills has said that she will consider increasing state support. For Maine Family Planning, Medicaid and Title X funding made up at least 40 percent of its budget last year, and state funding about 10 percent. Clinic leaders are also appealing to donors.

“But we’re not New York City,” said George Hill, Maine Family Planning’s president and chief executive. “We don’t have access to the same level of support as providers in more prosperous areas of the country.”

Several federal lawsuits are seeking to overturn the funding cut, including one filed by Planned Parenthood and another by a group of 21 Democratic-led states. The states have argued that the cut was unconstitutional because it singled out one entity, Planned Parenthood, for harm.

In Maine, access to health care varies widely between the state’s more populous southern cities and its vast northern reaches. Rural residents have poorer health overall and are less likely to have insurance, research has found.

Two of the three clinics where Maine Family Planning had established full-fledged primary care operations are in Aroostook County. The county is state’s northernmost region, about the size of Rhode Island and Connecticut combined, spanning 6,800 square miles, and one of its most medically underserved areas.

At a clinic in Ellsworth, nurse practitioners work with the local homeless shelter to provide mental health care for unhoused people. At another, in Thomaston, a new program had been set to launch this month, providing medication treatment to patients with substance abuse disorders.

Ms. Shields-Haas, who works at the Thomaston clinic, said it felt deeply unfair that her patients will lose access to badly needed care.

“These are hardworking people who are hauling lobster traps or taking care of your second home, under incredible financial pressure,” she said. “They pay taxes for this care.”

The newest Maine Family Planning clinic, a roaming van equipped with a miniature lab, was parked near a bridge in Augusta, the state capital, one morning last month, just uphill from a riverfront encampment. Josh Wheeler, an emergency medical technician who drives the van, described how he had spent 90 minutes talking with a man at another recent stop, slowly building trust before persuading him to accept treatment for a severely infected leg wound.

Mr. Wheeler paused to offer a fist bump to another man who approached the van, encouraging him to help himself to free nail clippers and socks piled on a table nearby.

Ellen Taraschi, a nurse practitioner with the mobile clinic, said its work in the past year had begun to stabilize the health of its high-risk patients.

“When we started, there were so many urgent needs,” she said, “and now that has calmed down because we’ve been chipping away, treating infections, keeping people out of the E.R.”

She added, “The health care system here is so fragile. The more burden you can take off it, the better.”

One of the state’s largest health care providers, Northern Light Health, closed a hospital in Waterville and a clinic in Bangor in May, and cut its work force by 300 last month. Adding to concerns about access, a protracted contract dispute between the company and one of the state’s largest insurers, now in mediation, could force 30,000 patients statewide to seek new in-network providers.

Ashley Smith, who works in the restaurant industry and pays for her health care out of pocket, said the affordable care she had received at Maine Family Planning had ranged from treatment for a rare premenstrual disorder to a physical she had urgently needed to qualify for a job.

“I should be sending them Christmas cards, for the ease of mind they’ve given me,” said Ms. Smith, who lives near Augusta, in the central part of the state.

Bethany Jarvis, a longtime nurse at the Ellsworth clinic, where some patients have been with her for decades, said recently that she had not yet begun preparing them for the primary care phaseout.

“To be honest, I’m avoiding it,” she said. “Those are hard conversations, for me and for them.”