Pramila Jayapal is a first-term congresswoman from one of the most progressive districts in Washington state. As such, it might seem easy to dismiss the political action committee she started in September, called Medicare for All Pac. That would be a mistake.

Jayapal is one of hundreds of Democrats now running on single-payer healthcare, a monumental shift to the left for the party which – even when it controlled Congress and the White House in 2009 – passed a health policy overhaul which buttressed the private insurance system for almost a decade – Obamacare.

“We did a poll in swing districts,” said Jayapal, “The numbers were off the charts.” Not only did the Pac’s survey find liberals supported Medicare for All, she said, but “independents responded incredibly well.”

A recent survey by the union National Nurses United found 225 Democratic candidates in the House running explicitly on single-payer healthcare.

“It is a very, very popular policy, and it’s popular out of necessity,” said Jayapal. “People see what we have just doesn’t work. It’s costing way too much.”

“Medicare for All” refers to the popular public health insurance program for the elderly, called Medicare. Passed in 1965 with Medicaid, its sister program for the impoverished and disabled, the single-payer program covers all Americans older than 65, and many more who are disabled.

Along with other public health insurance programs, such as for veterans, the military and Native Americans, the US already provides health insurance for nearly 100 million people, said Chris Sloan, a director at the health consulting company Avalere.

“Public opinion has shifted.,” he said. “That is why [healthcare has] become more of a defensive issue for Republicans and an offensive issue for Democrats”.

Democrats who support Medicare for All are some of the party’s most recognizable figures – Alexandria Ocasio-Cortez; Senators Bernie Sanders, Elizabeth Warren and Kamala Harris, and the former New York gubernatorial candidate and actor Cynthia Nixon.

Meanwhile, Republicans who have attacked the policy online have been roasted by advocates. When Representative Paul Ryan recently tweeted Medicare for All would “destroy and obliterate the private health insurance system”, one user responded: “Yes, that’s why we want it”.

Single-payer, government-run health care would essentially destroy and obliterate

→ the private health insurance system,

→ the employer-sponsored health insurance system,

→ oh and by the way—Medicare as we know it. pic.twitter.com/83fExtgIBF — Paul Ryan (@SpeakerRyan) October 22, 2018

The US has the world’s most expensive health system. Where the UK spends about 9.8% of GDP on healthcare, the US spends a whopping 17.9%, or more than $10,000 per person per year. Most Americans get insurance through an employer. Even after Obamacare’s reforms, 28 million people are uninsured.

Insurance is so integral to financial stability in America, people make career decisions based on health insurance and delay retirement to maintain health insurance. Conversely, serious illness can also drive people into personal bankruptcy.

Even people who have insurance can face steep costs. The average American worker pays $5,547 a year in monthly health insurance fees and more than $1,500 in once-a-year fees before insurance even begins to cover complex or expensive care.

Further, the opacity of American healthcare leaves patients with “surprise bills” after they get to hospital, use an ambulance or have surgery.

As just a few examples: a Texas hospital sent a man a bill for more than $108,000; a New Jersey woman owed more than $51,000 after the premature birth of triplets; and an injured doctor taken to hospital via air ambulance owed more than $56,000 to the helicopter company. All of those patients had health insurance at the time they incurred those bills.

Financial strain is particularly acute for the seriously sick. A recent study from the Commonwealth Fund, a foundation which promotes affordable healthcare, found of people with serious illnesses, 62% felt “confused and helpless”, 53% faced the “risk of financial ruin”, and 61% experienced “serious problems with their care”.

Some international figures have expressed exasperation with the American system of privately financed care, the only one in the industrialized world which lacks universal health coverage.

“It’s not easy to understand why such a country like the United States, the most resourceful and richest country in the world, does not introduce universal health coverage,” Ban Ki-moon told the Guardian. “Nobody would understand why almost 30 million people are not covered by insurance.”

Advocates believe patients’ financial strains, the threats of returning to a pre-Obamacare era and the spiking costs of health insurance have all led to Medicare for All to pick up steam.

Proposals differ among candidates. In some instances, it would more closely resemble the UK’s National Health Service. In others, it might include an expansion of Medicare, which people could purchase.

Further, many other Democrats are running on “universal coverage” rather than Medicare for All. Policies which promote universal coverage usually focus on shoring up the Affordable Care Act (Obamacare), or expanding Medicare to cover more people – just not everyone.

That debate is well reflected in a policy document from Community Catalyst, a centrist healthcare advocacy group. The group put out a guide on how to deal with single-payer advocates who “are strongly critical of any other alternative”, and fail to acknowledge single-payer is “not politically viable at this time”.

“Right now, Medicare for All and Medicare-for-more are proposals, but they’re missing key details,” said Sloan. “When that stuff gets filled in, it gets a little more controversial.”

Nevertheless, even with internal division, Jayapal believes the issue is at the heart of current politics and is not going to go way.

“Every time I send out an email to my campaign list on Medicare for All, it would go crazy. Every email resonates incredibly well, so we just knew we had something real here,” Jayapal said. “Medicare for All will be one of the most defining – if not the defining – issue of the 2020 presidential [election].”