JPecha/iStockBy DEVIN DWYER, ABC News

(WASHINGTON) -- In the midst of a pandemic and without an alternative health plan of its own, the Trump administration formally called on the U.S. Supreme Court to completely strike down the Affordable Care Act.

The administration makes the case in a legal brief filed Thursday in the case brought by 20 Republican-led states that want to completely invalidate the law.

The justices will hear oral arguments as soon as October, which is just weeks before the general election.

Two lower federal courts have ruled that the ACA’s individual mandate is unconstitutional after the GOP Congress in 2017 zeroed out the penalty for going without health insurance. Both courts called into question the viability of the entire law without the mandate.

“The individual mandate cannot be severed from the remainder of the ACA,” writes Trump solicitor general Noel Francisco. “The entire ACA thus must fall with the individual mandate.”

California and 19 other Democrat-led states are defending the law.

Former Vice President Joe Biden defended Obamacare Thursday at a campaign stop focused on health care, saying doing away with the ACA during a pandemic could be particularly harmful to many that need health care the most.

"I think it's cruel. It's heartless. It's callous. And it's all because, in my view, he can't abide the thought of letting stand on one of President Obama's greatest achievements, the Affordable Care Act," Biden said of the administrations' lawsuit.

Biden warned those who have survived COVID-19 and have subsequent health issues could be especially at-risk.

"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 said.

The ACA has sharply reduced the number of uninsured Americans since 2010, covering 20 million more people than if the law had not taken effect, according to the nonpartisan Kaiser Family Foundation.

Speaker of the House Nancy Pelosi issued a statement late Thursday night, calling the Trump administration's decision "unfathomably cruelty" to "rip away the protections and benefits of the Affordable Care Act in the middle of the coronavirus crisis."

"There is no legal justification and no moral excuse for the Trump Administration’s disastrous efforts to take away Americans’ health care," she said.

Industry groups and independent health care analysts say abruptly wiping out Obamacare would mean a highly disruptive shift in the health care of millions of Americans.

An estimated 52 million Americans have preexisting health conditions that insurers could have denied coverage to under pre-ACA rules in most states, the foundation said.

Preexisting condition protections and Obamacare insurance subsidies remain in place, for now, as the case continues, but could be at risk.

The case marks the third time the justices will consider the constitutionality of the Affordable Care Act since it was signed by President Barack Obama in 2010. Chief Justice John Roberts in 2012 famously cast the decisive vote, siding with the court's liberal justices to uphold the law.

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