Democrats are seizing on the spread of the coronavirus to emphasize what they see as a major vulnerability for President Trump on an issue voters consistently rank as a top concern: health care.

Republican efforts to undo the Affordable Care Act, including a current Supreme Court case, were already central to Democratic argument that Trump is sabotaging the health system, and they contend that the spread of a mystifying global pandemic only strengthens that case.

“How could it be that when we spend so much more than what other countries are spending, we have millions of people who may be dealing with the virus but they cannot go to the doctor because they can’t afford it?” Sen. Bernie Sanders (I-Vt.) said Friday. “What this crisis is beginning to teach us is that we are only as safe as the least insured person in America.”

Trump, who has spent recent weeks meeting with executives from the health-care industry, has struggled with the issue since Republicans in 2017 failed to repeal the ACA, falling short on a repeated campaign promise. Instead, the effort boosted the popularity of the ACA, also known as Obamacare, and Democrats notched major victories in the 2018 midterms by criticizing the GOP on health care.

Last week, former president Barack Obama released a video message to supporters highlighting the upcoming 10-year anniversary of the ACA, saying that Republicans are still seeking ways “rip away the care that millions of Americans rely on.”

The number and proportion of Americans without health insurance grew in 2018 for the first time in a decade, according to the most recent census figures. The figures showed that the uninsured rate increased to 8.5 percent from 7.9 percent the year before. More than 27.5 million U.S. residents lack coverage.

Many critiques of Trump’s handling of the outbreak have focused on competence. As Democrats turn to health care, they are zeroing in on issues such as the Trump administration’s decision to allow the sale of cheaper insurance policies that provide less coverage, saying it gave Americans more choice.

But Sen. Patty Murray (D-Wash.) said at a recent committee hearing that such policies are not required to cover tests or vaccines, which makes it “much harder for people to get the care they need to keep this crisis under control.”

The White House disagrees, pointing to moves by the administration that encourage insurance companies to provide free coronavirus testing. On Friday, Trump gave his support to bipartisan House legislation that provides free coronavirus testing for uninsured people.

Trump claimed credit for the provision, though it was pushed by Democrats who have long criticized his administration for not doing enough to protect the uninsured. “This Bill will follow my direction for free CoronaVirus tests,” Trump tweeted on Friday.

During a news conference in the White House Rose Garden, Trump also said his administration was working with Google to build a screening website for Americans looking for information about testing. Still, within hours, several discrepancies emerged between the White House and Google versions of what the site will be able to do, where it will do it and when.

Both Sanders and former vice president Joe Biden, the major contenders for the Democratic presidential nomination, have been making regular statements on the outbreak, seeking to contrast their approach with Trump’s. Sanders in particular says that the pandemic demonstrates the need for Medicare-for-all, his universal coverage plan, under which testing and vaccines would be free.

Biden, for his part, touts ACA’s success in increasing coverage and has promised to add a government-run “public option” that Americans could sign up for if they want.

Trump has blasted Sanders’s Medicare-for-all plan as unworkable and overly expensive, and his campaign says Biden’s less ambitious plan would also raise costs for taxpayers. Trump’s allies, meanwhile, have been touting the president’s record on health care in recent weeks, citing efforts to increase funding for opioid treatment and actions to increase transparency in medical billing.

“President Trump offers the American public lower costs, more choice, and better care, along with ensuring care for Americans with preexisting conditions,” campaign spokeswoman Kayleigh McEnany said in a lengthy statement highlighting Trump’s record.

White House spokesman Judd Deere added that Democrats are pushing “radical plans” that would take health care away from millions of Americans.

“Under the previous administration, Americans saw their premiums skyrocket, and it was the Trump administration that stabilized the market, giving consumers certainty,” Deere said.

But Democrats see a vulnerability. At a campaign rally in St. Louis on Monday, Sanders seized on Health and Human Services Secretary Alex Azar’s reluctance to promise that a coronavirus vaccine would be available to the public at an affordable price.

Sanders did not mention Azar by name, but he noted that “Trump’s people” have said they can’t guarantee the vaccine’s affordability, prompting boos from the crowd.

“I mean, this is how sick the system is. So let me tell you, [when I’m] elected president, everybody in this country will get that vaccine absolutely free,” Sanders said to cheers.

Azar said in a letter to Congress that the government would work with the private sector to ensure that the vaccine is affordable.

As the Supreme Court prepares to hear arguments in the ACA lawsuit, Trump has opted not to release a replacement health-care proposal should the law be thrown out. He has said he would put forward comprehensive health-care legislation only after the upcoming election, and only if Republicans regain full control of Congress. A final ruling from the Supreme Court could come next year.

That follows a dramatic turnaround in the politics of health care. After the enactment of the ACA in 2010, Republicans regularly denounced it as government overreach, pledging to overturn it at the earliest opportunity.

But when Republicans won unified control of the government in 2016, they were unable to come up with a replacement or muster the votes to repeal the health law. Instead, as more Americans became alarmed at the notion of losing the ACA, its popularity increased.

Now the administration’s shaky handling of the coronavirus outbreak is further alarming some Republicans, given that pollsters regularly find health care at the top of voters’s concerns.

In response, the president and his team have been trying to reassure the public, holding regular news conferences on the outbreak. “Anyone who wants a test can get a test,” Trump said earlier this month, though that was later contradicted by other officials.

The lack of adequate testing kits, a problem acknowledged by the Centers for Disease Control and Prevention, reflects the flawed response by the Trump administration, said Ben Sommers, a doctor who teaches at the Harvard T.H. Chan School of Public Health. Trump’s attempts to weaken the ACA will make it harder for people to access the tests once they become widely available, he said.

“People have to come forward and get tested,” Sommers said. “Getting referred by seeing doctors or nurses who say, ‘Yep, this is a patient who is at risk and needs to be tested’ — that doesn’t happen when someone is scared to get health care because they can’t afford it.”

A spokesperson for the Department of Health and Human Services said the decision on whether to charge for coronavirus testing will be made by the states. People without insurance can receive care at community health centers at a reduced cost or free, the spokesperson said.

Congress and the administration, as well as the states, have spent weeks grappling with how the uninsured will get treatment amid the coronavirus outbreak. Some Republicans have joined Democrats in calling for the government to provide not only free coronavirus testing but also treatment for the uninsured.

“You can look at it as socialized medicine,” Rep. Ted Yoho (R-Fla.) told digital news site HuffPost earlier this month. “But in the face of an outbreak, a pandemic, what’s your options?”

Trump has publicly complained about how his record on health care is viewed by voters. At a March 5 town hall in Pennsylvania, he answered a question about health care by saying his accomplishments had not gotten their due.

“It’s a great question and very important — health care,” he said. “And I think it’s probably the thing that I’m most disappointed that I haven’t been able to say what a good job we’ve done. I haven’t been able to sell what a great job we’ve done.”

During a meeting last week with insurance executives, Trump used his televised remarks to talk about his efforts to help the cruise industry and airline industry. He spoke only briefly about health care.

Heather Kelly, Felicia Sonmez, Erica Werner and Mike DeBonis contributed to this report.