Rep. James Clyburn (D-S.C.), left, watches as Sen. Bernie Sanders (I-Vt.) speaks about health care on Capitol Hill in late June. (Drew Angerer/Getty Images)

Randy Bryce, an ironworker and labor organizer challenging Speaker Paul D. Ryan for his Wisconsin House seat, was having a good week. His campaign, kicked off by an emotional video, raised nearly $500,000 in less than 30 days.

This week, Bryce beamed into CNN to keep up the momentum — and ran straight into a question about whether he, like a growing number of Democrats, supports European-style universal health care.

“You want to raise $32 trillion in taxes?” CNN’s John Berman asked.

“There’s a lot of people not paying their fair share in taxes,” Bryce said. “There’s corporations getting away with a lot.”

“That would be quite a tax hike,” CNN’s Poppy Harlow said. “That’s an astonishing number, $32 trillion over a decade.”

Democrats, who are largely using the week-long recess to rally opposition to the Republicans’ deeply unpopular attempt to repeal parts of the Affordable Care Act, are now facing a political challenge of their own: increasing pressure from their liberal base to embrace universal, government-funded health-care coverage.

Sen. Bernie Sanders (I-Vt.), perhaps the country’s most prominent proponent of universal coverage, is waiting for an opening — likely after the GOP’s repeal push succeeds or fails — to introduce a new bill. Sens. Elizabeth Warren (D-Mass.) and Kirsten Gillibrand (D-N.Y.), both seen as potential 2020 presidential candidates, each said last week that the party needed to get behind “Medicare for all.”

Republicans have noticed — and have begun to attack. Facing a widespread voter backlash over the House and Senate repeal bills, they’re trying to make universal coverage a political anchor for Democrats by asking whether they can seriously defend trillions of dollars in new taxes and spending.

On Wednesday, the GOP’s Senate campaign committee launched Web ads against the 10 Senate Democrats up for reelection in Trump-won states, warning of “government health care” if they win. The same day, the National Republican Congressional Committee gleefully highlighted the CNN interview with Bryce. White House press secretary Sean Spicer has also chimed in.

“When you look at the majority of House Democrats, they support a single-payer, $32 trillion bill backed by Bernie Sanders,” Spicer said last month. “We need to accept that Obamacare is dead, we need to understand that the reality is that what the choice is is between putting in a system that is affordable and accessible, or a single-payer $32 trillion health-care plan that the majority of House Democrats support.”

The $32 trillion refers to H.R. 676, a Medicare-for-all bill sponsored every year by Rep. John Conyers Jr. (D-Mich.); the cost estimate comes from a study by the Urban Institute. For the first time, most House Democrats have endorsed the bill, and many can explain how a single-payer system would end up saving money.

(Jenny Starrs/The Washington Post)

Still, Republicans are readier to attack the measure than many swing-district Democrats are ready to defend it.

“I continue to be surprised, though perhaps I shouldn’t be, that they keep moving further and further left, especially after getting burned politically by Obamacare for so long,” said Rob Engstrom, the political director of the U.S. Chamber of Commerce. “Where are the days where Rahm Emanuel and Howard Dean would come in and find moderate candidates that could actually win in the South and West?”

Sanders’s upcoming bill will have a lower price tag and cost-sharing measures that will be easier to sell, according to aides. But any single-payer plan will require a tax increase larger than any on which Democrats have run since the Great Depression. In 2016, Sanders proposed paying for his plan with a 2.2 percent federal income tax hike and a 6.2 percent health-care payroll tax on employers. Some red and purple state Democrats, including Sen. Joe Manchin III (D-W.Va.), have blanched at the cost.

“I told Bernie this: Let’s look at the tax code,” Manchin said in a recent interview with The Washington Post. “Look at Sweden and Denmark — look at their tax code. You can’t just pick what you like and think everything stays the same. How are you going to pay for it? How do people get access to it? How much regulation? Let’s find out.”

Democrats, and Sanders, saw the attack line coming months ago. On one hand, as activists constantly remind them, “Medicare for all” polls better than either party’s current health-care positions. Last month, a new study from Pew Research found 60 percent of all voters agreeing that it was “the federal government’s responsibility to make sure Americans have health coverage.” Thirty-three percent of all voters favored a single government insurance system; among Democrats, the number rose to 52 percent, having grown every year since the ACA’s passage.

The single-payer chorus has been growing louder, too. Gillibrand has talked about expanding Medicare for years, but it was only last week when she fully embraced a single-payer, government-funded model. Bryce is among the new faces on board.

Last week, as Sen. Kamala D. Harris (D-Calif.) addressed a pro-ACA rally outside the Capitol, members of Democratic Socialists of America chanted “single payer!” As Sen. Ron Wyden (D-Ore.) finished his first town hall meeting of the recess, a 35-year-old Web developer named Justin Speers demanded that he talk about the Conyers bill.

“Senator Wyden!” Speers shouted. “Will you support Medicare for all, H.R. 676, and quit taking money from Blue Cross/Blue Shield?”

When the applause died down, and the handmade “Medicare for all” signs were lowered, Wyden passed the litmus test — barely — by talking about how states could build single-payer systems under the existing structure of the Affordable Care Act.

“Democrats need to stand for something, or they will keep getting crushed,” Speers said. “The least they can do is stand for Medicare for all.”

Some liberal activists are skeptical that all the Democrats now willing to talk about universal coverage are also willing to act on it.

In states dominated by Democrats, single-payer campaigns have been thwarted by the high cost estimates — a preview, some worry, of what would happen if the plans went national. In 2014, Sanders’s own Vermont, run entirely by Democrats, bottled a single-payer plan that would have been paid for by a 11.5 percent tax on businesses and 9.5 percent premium assessment.

“The total cost would still have been lower even with expanded access with better coverage,” said Deb Richter, the Vermont director of Physicians for a National Health Program. “But you need to get the money from different pockets. And those pockets have influence, whereas those who would benefit the most from single payer don’t have political clout.”

This year in California, progressives got a single-payer outline through the state Senate, where Democrats hold a supermajority. But the state’s budget rules would have required a state referendum or a yearly supermajority vote to pay the estimated $400 billion annual bill. House Democrats blocked a vote on the single-payer plan, which kicked off protests led by the California Nurses Association and a coalition of single-payer groups. RoseAnn DeMoro, the executive director of CNA, said Democrats were running on single-payer without ever planning to deliver.

“The Democrats will now co-opt the language of single payer for the wrong reasons, like Levi’s co-opted blue jeans,” DeMoro said. “The question should be ‘do you support taking the insurance industry out of health care?’ That is where the rubber meets the road. And that’s where they will run for cover, with few exceptions.”

Sanders himself has offered Democrats a get-out-of-jail-free card, relaxing his 2016 campaign rhetoric to argue for a more gradual path toward single payer.

“Short term, we should lower the age of Medicare eligibility to 55 years of age,” Sanders said in a weekend interview with CNN. “In the short term, I hope we can work with Republicans to end the absurdity of us paying the highest prices in the world for prescription drugs. Longer term, we need a Medicare for all system.”

Democrats are also willing to provide leeway for candidates who didn’t run on universal coverage. In this year’s special House elections, only one Democrat, Montana’s Rob Quist, said he favored Medicare for all. None of the others faced a serious backlash from activists, who were hungry for a win.

“Sure, Republicans are going to attack, but I think we’ll just have to defend,” said Rep. Keith Ellison (D-Minn.), a co-sponsor of H.R. 676 and deputy chairman of the Democratic National Committee. “If they’re right, why does every other country in the industrialized world pay half as much as we pay and have better health-care costs? Explain, how does the VA do this? How does Medicare do this? It’s not like Americans don’t have a clear concept of single-payer; it’s called the VA, and it’s called Medicare.”

Ellison added: “If they don’t believe in having a Medicare-for-all system, I don’t want them to get up and say they do,” Ellison said. “But I’ll tell you this — if you’re a Democrat looking for an applause line, get up and say something about Medicare for all.”