The far-reaching impact of invalidating the law cannot be overstated. Even Republican health efforts — including many Trump administration initiatives — would be threatened by the disappearance of the ACA.

There was a brief lag between O'Connor's opinion and the Democrats' appeal because the judge did not issue last month's ruling as a formal, final decision, given it didn't address other aspects of the GOP challenge. At the request of the Democratic attorneys general, on Dec. 30 the judge finalized his findings for this part of the case, and clarified that the law would remain in effect during the appeals process.

Separately, the brand-new Democratic majority in the U.S. House voted to support the appeal of the decision on their first day in charge of the chamber.

They approved language authorizing House Speaker Nancy Pelosi “to intervene, otherwise appear, or take any other steps in any other cases involving the Patient Protection and Affordable Care Act,” better known as the ACA.

House Democrats also filed a motion to intervene in the defense of the ACA against the GOP-led lawsuit.

Republicans on the House floor were not impressed. “That effort does not preserve preexisting conditions,” Rep. Greg Walden (R-Ore.), now the ranking member of the House Energy and Commerce Committee, said on the floor. Walden, who helped lead the GOP's unsuccessful “repeal-and-replace” effort in the last Congress, suggested that lawmakers should instead pass a law reaffirming the preexisting condition protections.

Some backers of the law agreed with Walden. “The House should pass a bill. Send it to the Senate. See what happens,” tweeted University of Michigan law professor Nicholas Bagley.

In an op-ed written with fellow Michigan law professor Richard Primus, Bagley said Congress could more effectively remove the legal threat to the law by raising the mandate penalty to a dollar, by repealing the mandate entirely or by clarifying that eliminating the mandate penalty does not require the invalidation of the rest of the law.

“Any of these solutions could be accomplished in a one-sentence statute, and any one of them would end the Texas lawsuit,” they wrote.

California Healthline's California politics correspondent Samantha Young contributed to this report.

Kaiser Health News (KHN) is a national health policy news service. It is an editorially independent program of the Henry J. Kaiser Family Foundation which is not affiliated with Kaiser Permanente.

Read more:

• ACA litigation and 3 other policy issues to watch as Democrats take the House
• 5 possible consequences of the Texas ACA ruling
• GOP candidates playing defense on Obamacare