WASHINGTON, D.C. - The future of health care for millions of Americans is back in the hands of the judicial system.

On Tuesday, a federal appeals court in New Orleans is hearing whether or not the Affordable Care Act is unconstitutional.

An estimated 133 million Americans with pre-existing conditions are covered under the A.C.A, and an estimated 20 million Americans still have health insurance through the Obama-era law.

“This case is every bit of a threat to health care as the repeal bills were in 2017,” U.S. Sen. Bob Casey (D-Pa.) said.

Casey backed the bill when it went through Congress in 2010. Now, he fears the 5.3 million Pennsylvanians – nearly 1 in 2 residents – with a pre-existing condition could lose protections under the law. That includes 640,000 Pennsylvania children.

“We’re not going to stand for allowing children to go uncovered because some politicians in Washington failed in their repeal effort and are now using the courts to rip away health care,” Casey said.

The case comes after Republicans failed to overturn the A.C.A. in 2017. On the steps of the U.S. Senate, top Democrats are held posters showing the faces of Americans who could lose coverage.

“We are gathered because this is a critical day for health care in America,” said Senate Minority Leader Chuck Schumer (D-N.Y.)

The basis of this case actually started in Congress in late 2017 when Congressional Republicans eliminated the so-called "individual mandate" that forced Americans to have health insurance. Because the mandate in the A.C.A. was valid under Congress’s taxing power, critics argue removing the tax makes the rest of the law unconstitutional. Democrats and supporters of the A.C.A. are arguing that isn't the case.

Republicans have already gained a win in their effort to repeal the law. In December, a lower court ruled the A.C.A. unconstitutional on those grounds. If the federal appeals court does the same, this case could head to the U.S. Supreme Court during next summer’s heated 2020 presidential race.