Presumptive Democratic nominee Joe Biden and House Speaker Nancy Pelosi (D-Calif.) mounted a fresh assault on President Trump’s efforts to kill the Affordable Care Act on Thursday, accusing Trump of putting Americans’ lives at risk during a pandemic.

At a campaign trip to the crucial battleground state of Pennsylvania and on Capitol Hill, Biden and Pelosi sought to heighten public attention to the sprawling health-care law that brought insurance to millions of Americans.

The remarks were timed to coincide with the filing of legal briefs by the Trump administration and Republican attorneys general in a major lawsuit trying to rescind the ACA.

The signature domestic achievement of President Barack Obama has been a whipping post for Republicans — and a point of pride for Democrats. The insurance marketplaces created by the ACA and its expansion of Medicaid have helped insure 20 million Americans. And they’ve assumed new importance in recent months as the coronavirus has devastated the U.S. economy, causing people to lose jobs and the health benefits that came with them.

In his remarks, Biden said that some coronavirus survivors could lose their comprehensive health-care coverage if the lawsuit to overturn the ACA is successful. He also said that if the law were invalidated, insurance companies could refuse ongoing coverage of those with covid-19, deeming it a preexisting condition.

“Those survivors, having struggled and won the fight of their lives, would have their peace of mind stolen away at the moment they need it most,” Biden said. “They would live their lives caught in a vise between Donald Trump’s twin legacies: his failure to protect the American people from the coronavirus, and his heartless crusade to take health-care protections away from American families.”

Biden also railed against Trump’s handling of the coronavirus.

Trump is “like a child who can’t believe this has happened to him. All his whining and self-pity,” Biden said. “Well, this pandemic didn’t happen to him. It happened to all of us. And his job isn’t to whine about it, his job is to do something about it.”

Trump has stated repeatedly that he would protect preexisting conditions, though his administration has not presented any policy proposals for how it would do so. Ahead of Biden’s event on Thursday, the Trump campaign ridiculed Biden for supporting a public insurance option, which would allow Americans to buy into a government health-care plan such as Medicare.

“The public option would be a disaster, and really all it is is opening the door to a government monopoly on health care,” Tim Murtaugh, the communications director for the Trump campaign, said on a conference call with reporters. “It limits choices and reduces quality.”

Health care was a central issue during the Democratic primaries, one that pitted Biden, who wants to expand the ACA, against the more liberal wing of the party, which called for a fulsome embrace of Medicare-for-all, a ­single-payer system.

Now that he is the presumptive nominee, Biden’s campaign has developed a general-election strategy that tries to rally the public around universal health-care coverage. He has argued that a public option is now vital as unemployment increases and people lose their employer-based health-care coverage.

He said Thursday that he will outline a new proposal “in the next few weeks” to guarantee that no one would have to spend more than 8.5 percent of their income on health insurance. Poor Americans would pay even less.

During a Tuesday night fundraiser with Obama, the duo argued for building on the original measure. “Obamacare, the Affordable Care Act, was always designed, as has been true with all major big social welfare initiatives, to be a starter home, a foundation to build off of,” Obama said. “We know it was imperfect. It was what we could get at the time.”

On Capitol Hill, Pelosi appeared to do just that, introducing a bill Wednesday that would broaden the reach of the ACA and make it available to more Americans. Criticizing Trump, she said that trying to overturn the health-care law “was wrong at any time. . . . Now, it is beyond stupid. Beyond stupid.”

The bill would penalize states that do not expand Medicaid and expand subsidies for people who buy private health plans in the insurance marketplaces created under the law for individuals and families who do not have access to affordable health-care benefits through a job.

“The pandemic, of course, points out the further need to make [health care] more affordable and accessible,” she said during a Thursday interview with Washington Post Live.

The latest legal battle over the law moved forward Thursday in the Supreme Court, with each side filing briefs largely restating the arguments that persuaded the court to take the case.

The lawsuit was initially considered unlikely to gain much traction, and even some legal scholars who oppose the ACA thought its arguments were weak. Its central argument is that a change in tax law, eliminating a penalty for people who flouted a requirement that most American carry health insurance, meant the law’s insurance mandate no longer had a constitutional basis — and so the whole law was invalid.

In December 2018, a conservative federal district judge in Texas ruled the entire law unconstitutional nationwide. The law has stayed in place during appeals. Last December, a New Orleans-based federal appeals court ruled that the insurance requirement — which Congress had by then eliminated — was unconstitutional. The appellate judges sent back to the lower court the question of whether the rest of the law could remain intact.

In January, a coalition of Democratic-led states, the parties in the case trying to preserve the law, asked the Supreme Court to review it, and the court took the case in March. The court has twice upheld the law’s constitutionality.

Two years ago, when the Trump administration decided not to defend the existing law against a legal challenge, Justice Department officials argued that the ACA provision requiring most Americans to carry health insurance would soon no longer be in place. As a result, they argued, consumer insurance protections under the law would not be valid, either.

At the time, the administration argued that many other aspects of the law could survive because they could be considered legally distinct from the insurance mandate, and consumer protections such as a ban on charging more or refusing coverage to people with preexisting medical conditions.

The administration later hardened its position, joining Republican attorneys general in contending that the entire law must be considered invalid.

In a 49-page brief plus an appendix filed late Thursday night, Justice officials maintained their harder legal stance. “The individual mandate cannot be severed from the remainder of the ACA,” said the brief, signed by U.S. Solicitor General Noel J. Francisco and other Justice attorneys. And when a Republican Congress adopted tax legislation in late 2017 that eliminated the ACA’s penalty for not having insurance, “Nothing the 2017 Congress did demonstrates it would have intended the rest of the ACA to continue to operate in the absence of these . . . integral provisions.”

Pelosi immediately issued a tough response to the brief. “President Trump and the Republicans’ campaign to rip away the protections and benefits of the Affordable Care Act in the middle of the coronavirus crisis is an act of unfathomable cruelty,” she said in a statement.

California Attorney General Xavier Becerra, leading the Democratic attorneys general trying to preserve the law, said in a statement: “The death toll from the coronavirus today is greater than the death toll of the Vietnam War. The ACA has been life-changing and now through this pandemic, we can all see the value in having greater access to quality healthcare at affordable prices. Now is not the time to rip away our best tool to address very real and very deadly health disparities in our communities.”

The Center for American Progress, a liberal-leaning think tank, released a letter to Trump on Thursday signed by nearly 800 public health officials beseeching his administration to reverse its support for the lawsuit, California v. Texas, lodged in early 2018 by Texas Attorney General Ken Paxton (R) and nearly 20 GOP counterparts. The seven-paragraph letter contends that the prospect of losing the insurance gains could fall particularly hard on essential workers in health-care settings and grocery stores who have been affected by the coronavirus.

“If the Supreme Court effectively overturns the ACA with your assistance, imperiling the health insurance of the millions who have risked their lives for the rest of us during this pandemic, it will be a cruel thanks for their sacrifice,” the letter says.

Earlier in the week, the center issued a new analysis predicting that more than 23 million Americans would lose health benefits if the law were struck down. The estimate is about 3 million higher than previous ones.

Meanwhile, the Kaiser Family Foundation, a nonpartisan health research organization, issued an analysis Thursday that finds 4.7 million people in the United States would become eligible next year for Medicaid, the public insurance safety-net program, if 14 states that have not expanded the program to people with slightly higher incomes, as the ACA allows, chose to do so.

The analysis estimates that 1.9 million of those people are suddenly at risk of losing health benefits because they have lost a job during the pandemic.

In choosing Lancaster, Biden’s campaign set his Thursday afternoon event in a county that Trump won by about 20 points in 2016. Trump protesters gathered outside and could be heard chanting “USA!” and “Four more years!” as Biden met in a courtyard with a group of families who have benefited from the Affordable Care Act.

“Hey guys, how are you?” Biden said as he arrived, to a group all wearing masks and practicing social distancing. “This is kind of strange, isn’t it? Nice to see you all.”

Biden told the group that he was worried that the Supreme Court would strike down the ACA but expressed optimism his proposals could become law if he’s elected.

“If Donald Trump refuses to end his senseless crusade against health coverage,” Biden said during his speech, “I look forward to ending it for him.”