A group of Democratic attorneys general are appealing a recent federal court decision overturning Obamacare because the Trump administration has refused to defend the federal health care law.

A federal judge in Texas ruled last month that the Affordable Care Act is unconstitutional, finding that the law cannot stand now that Congress has rolled back the mandate that everyone carry health insurance or pay a fine. The case was brought by a coalition of Republican attorneys general.

The ruling poses a significant threat to the Affordable Care Act’s most popular and most sweeping health insurance reforms. If higher courts affirm the ruling, it could roll back Obamacare’s ban on preexisting conditions — which is why Obamacare supporters are aggressively fighting back.

Typically, the federal government would be defending a federal law. But the Trump administration has declined to do so, instead filing court briefings that support the Affordable Care Act’s repeal.

This has led a coalition of 17 pro-Obamacare attorneys general, led by California’s Xavier Becerra, to intervene on the health care law’s behalf, notifying the Fifth Circuit Court of Appeals on Thursday that they would appeal. Documents outlining the attorneys general’s legal arguments in the case will be submitted in the coming weeks and months.

“Not one state that is defending the Affordable Care Act was an original party to this litigation,” Becerra told reporters. “We didn’t believe the federal government would adequately defend the law in court. And I think we’ve been proven right.”

Texas Judge Reed O’Connor issued his sweeping ruling on December 14. Two weeks later, on December 30, he issued a stay that clarified that Obamacare remains fully in effect as this case works its way through the legal system.

Becerra said he “hopes” that the appeals process will finish by the end of 2019, potentially setting up a Supreme Court appeal in 2020 — right in the middle of the next presidential election.

While Trump has predicted that this case will ultimately go before the Supreme Court, the attorneys general did not see that as inevitable. The Supreme Court would ultimately need four justices to vote to hear the case for it to move forward.

“We’re going to take it wherever we need to take it,” he said.

Read the attorneys general’s notice of appeal here, and learn more about the Texas court ruling here.