CONCORD, N.H. — In a union hall a mile from New Hampshire's gold-domed statehouse, Joe Biden was working a rope line, taking selfies, clapping voters on the shoulder, when a woman with a red plaid dress and a message got her turn.

“Health care is so important,” Sheila Zakre told the former vice president running for the Democratic presidential nomination.

A 61-year-old disability rights lawyer who works on her own, Zakre is part of the insured middle class. Still, she and her husband, Bob Sanders, are fighting an unexpected $2,400 hospital bill after a facility fee was tacked on for a scan in a doctor’s office.

She is legally blind and holding off replacing her special glasses after they broke weeks ago because the $800 cost is not covered by the health benefits they get through his job. And though he turns 65 next month, he is thinking of working until she is old enough for Medicare, too, because, without his insurance, her premiums for an Affordable Care Act health plan would be nearly twice what they pay now.

“The Affordable Care Act is just not affordable for us,” she said.

This first-in-the-nation primary state is also at the leading edge of Americans’ frustration with flaws of the U.S. health-care system. In conversations as well as in standing-room-only audiences at town hall gatherings with the presidential candidates, the system’s flaws come up often: the expense of prescription drugs, a scarcity of mental health services, coverage gaps, care difficult to afford even for people with private insurance.

Some 28 percent of likely Democratic primary voters in New Hampshire consider health care the most important issue in deciding whom to vote for, according to a November Quinnipiac poll — the highest-ranking issue here, as well as nationwide, according to another Quinnipiac poll. Nearly half of New Hampshire Democratic voters said in a WBUR/MassINC poll last month that they want candidates to talk about health care — far surpassing any other topic.

With its tradition of presidential contenders meeting face-to-face with residents in relatively intimate settings, New Hampshire has a history of sensitizing candidates to the matters that are on its voters’ minds.

In 2008, a Service Employees International Union project printed purple T-shirts and stickers saying, “I’m a health care voter!” and made sure the purple was plentiful at New Hampshire primary events, recalled Concord City Council member Zandra Rice Hawkins, the executive director of Granite State Progress, an advocacy organization for which health care is a flagship issue. The project contributed to President Barack Obama’s rapid focus on what grew into the ACA, Rice Hawkins said.

And in 2016, when the opioid crisis had taken hold hard here, candidates heard from voters, in tears, about family members’ addictions and deaths.

Hillary Clinton attended a reception at the home of the New Hampshire state senate president and recounted having just met with the head of a company who had told her that 40 percent of his workers regularly failed drug tests he required, recalled Ned Helms, a longtime Democratic activist and former state health commissioner who founded the University of New Hampshire’s Institute for Health Policy and Practice. “I think it was an awakening,” Helms said.

“In this cycle, I don’t think I’ve been at a town hall meeting . . . where health care hasn’t come up on the part of the people,” said Helms, a Biden supporter who has attended events over the months by virtually every Democratic candidate. “People really want to know what you are going to do.”

Campaign gatherings here seem to be nudging the Democratic field beyond its running internal dispute over whether the country should shift to a single-payer health-care system. Candidates are bringing up mental health needs and the pain of worrying about medical bills on top of diagnoses. Republicans “always want to cut people’s health care because it’s too expensive to let people live,” candidate Tom Steyer said Wednesday night at a crowded town hall in a Manchester pub.

Fueling voters’ concerns, the state has “some of the highest costs — out-of-pocket costs and premium costs — in the region, and they continue to go up,” said Lucy Hodder, a UNH health law professor and former senior health-care adviser to then-Gov. Maggie Hassan (D), now a U.S. senator.

New Hampshire has the nation’s third-highest proportion of residents with job-based insurance that features a high deductible — the amount consumers must pay up front before their coverage begins.

“My own employees were avoiding getting care,” said Joanne Conroy, president of Dartmouth-Hitchcock Health, New Hampshire’s largest private employer. Last year, Dartmouth-Hitchcock began chipping in most of the money to health-savings accounts for lower-income workers and increased its contribution for employees with incomes of up to $150,000.

Even so, the costs can be overwhelming. Kat Barrell, a Dartmouth-Hitchcock marketing manager, discovered in the fall of 2016 that the pressure she had been feeling in the lower right side of her abdomen was a four-pound ovarian tumor — clear cell carcinoma. After chemotherapy, her doctors said she was cancer-free, but it returned last summer, and she began an immunotherapy clinical trial.

The trial pays for the drugs, but not the CT scans she needs every six weeks at $9,000 each, or the infusion or doctors’ appointments. Even with a health plan that she thinks is fair, she faces a $2,800 deductible for herself and her teenage son. (The premiums would double if she included her husband, Chris, so he is on a health plan with a larger deductible through his job as a horse farm’s maintenance technician.) And at the start of each year, she dreads her plan’s $4,400 out-of-pocket maximum. Together, Barrell and her husband, who recently had knee surgery, have racked up about $37,000 so far for the expenses their insurance is not covering.

Her husband is postponing rotator cuff surgery, wanting to focus on paying for her care even though he works every day in pain.

Barrell, 49, said she doesn’t think of herself as a political person, but that this year, “health care is number one on my hit list.” She has known she could not support a candidate who favors a single-payer system, fearing it could rupture relationships with her doctors. She has just decided to vote for former South Bend, Ind., mayor Pete Buttigieg, who sprinkles his town-hall events here with talk of a Medicare-like option for consumers who prefer an alternative to private insurance.

Like an uncommon number of voters with the primary so close, Zakre, the Concord lawyer, expects to make up her mind Tuesday with a pencil in her hand in the voting booth. She likes that Medicare-for-all would cover long-term care, since many of her elderly clients cannot afford it. And she thinks it would end the difficult conversation she and her husband keep having: She saying she might spare the expense of insurance by going uncovered if he retired, and he insisting he will keep working until she is old enough for Medicare, rather than leave her so vulnerable.

With one of the nation’s highest median ages and a fast-growing older population, the cost of prescription drugs is a major concern here. And people see close-up the limits of Medicare.

Michael Provost, 69, is part of a group of AARP volunteers, wearing crimson fleeces with white lettering saying “Stop RX Greed,” that has fanned out to candidates’ events, documenting what the candidates tell voters about their health-care plans. “As a widower, we have been financially devastated by my wife’s illness,” he told Buttigieg last Tuesday afternoon in an art space in Portsmouth.

Provost figures that, before he lost his wife of 36 years, Sylvia, in 2016, her five years of illness cost them more than $200,000 in bills that her Medicare did not cover. “It was a horror show,” he said. After cancer, then kidney failure and a stroke, “at a time she was supposed to be healing, she was worried” that they had to cash in her retirement savings and then his.

On Tuesday night, before Biden spoke and Zakre had her moment on the rope line, the candidate was introduced by Steve Shurtleff, speaker of the New Hampshire House of Representatives.

A year ago, Shurtleff, a Concord Democrat, formed a subcommittee to deal specifically with mental health. More and more often, he said, he hears of parents who can’t get a child into mental health treatment or drug rehab.

At a Biden town hall in Somersworth on Wednesday, Dee Perrotta, another of the crimson-fleece AARP group, was near the end of that rope line. A recently retired psychiatric nurse, she told the candidate that people can’t always afford medicines to treat their disorders. At the community health center in Essex where she worked, she and psychiatrists pleaded with insurance companies to approve drugs that were new or simply not ones they cover.

At a town hall in Derry with Sen. Bernie Sanders (I-Vt.), a college student holding a “Bernie” sign told him he has lined up a job as an insurance company analyst for when he graduates in May — and asked what would happen given that Medicare-for-all would wipe out private insurers. (“We will have a very just, unprecedented transition period,” Sanders replied.)

Underlying the candidates’ permutations — Medicare-for-all, Medicare for those who want it, a public option to improve the ACA — “it’s really universal health care people are aching for,” said Rice Hawkins, of Granite State Progress.

With nearly 45,000 New Hampshire residents having signed up for ACA health plans this year, and about 57,000 now covered through the ACA’s expansion of Medicaid, “once you start to use it, you start to peel back the onion,” Rice Hawkins said. “It can be tough, if you’re so excited to finally have health insurance, to realize there may be gaps.”

Helms, the longtime Democratic activist, said: “It’s emotional, and it’s financial. [Voters] get it in a very, very visceral way. And they want some assurance that the people asking for their vote have really thought about it.”

Scott Clement in Washington and Chelsea Janes and Sean Sullivan in New Hampshire contributed to this report.