FORT WORTH (CBSDFW.COM/CBS NEWS/AP) – A federal judge in Fort Worth on Friday ruled the entire Affordable Care Act is unconstitutional due to a recent change in federal tax law.

The move, coming on the eve of the deadline to sign up for coverage for 2019, leaves 20 million Americans’ health coverage in limbo.

The decision by U.S. District Judge Reed O’Connor is almost guaranteed to go to the Supreme Court.

The American Medical Association released the following statement after the federal district court in the Northern District of Texas sided with the plaintiff, striking down key provisions of the Affordable Care Act:

“Today’s decision is an unfortunate step backward for our health system that is contrary to overwhelming public sentiment to preserve pre-existing condition protections and other policies that have extended health insurance coverage to millions of Americans,” said AMA president Barbara L. McAneny, M.D. “It will destabilize health insurance coverage by rolling back federal policy to 2009. No one wants to go back to the days of 20 percent of the population uninsured and fewer patient protections, but this decision will move us in that direction.”

Texas Attorney General Ken Paxton applauded the decision.

“Today’s ruling enjoining Obamacare halts an unconstitutional exertion of federal power over the American health care system while our multistate coalition lawsuit works its way through the courts,” Attorney General Paxton said. “Our lawsuit seeks to effectively repeal Obamacare, which will give President Trump and Congress the opportunity to replace the failed social experiment with a plan that ensures Texans and all Americans will again have greater choice about what health coverage they need and who will be their doctor.”

In February, Attorney General Paxton and Wisconsin Attorney General Brad Schimel led a 20-state coalition lawsuit challenging the constitutionality of Obamacare, explaining that Congress rendered all of Obamacare unconstitutional by doing away with the tax penalty in Obamacare’s individual mandate when it enacted President Trump’s tax overhaul.

President Donald Trump tweeted, “As I predicted all along, Obamacare has been struck down as an UNCONSTITUTIONAL disaster! Now Congress must pass a STRONG law that provides GREAT healthcare and protects pre-existing conditions. Mitch and Nancy, get it done!”

Minutes later, Trump tweeted, “Wow, but not surprisingly, ObamaCare was just ruled UNCONSTITUTIONAL by a highly respected judge in Texas. Great news for America!”

Health Care Voter spokeswoman Mikka Macdonald released the following statement:

“There is nothing more American than ensuring that every citizen has access to the lifesaving and necessary health care they need. This ruling cements the fact that Republican leaders will stop at nothing to put the lives and livelihoods of America’s working families at risk to pursue their partisan agenda.

“In the midterm elections, the American people forcefully rejected Republican efforts to repeal and undermine the Affordable Care Act. And yet, Republicans have made it clear that their priority is attacking access to critically-needed health care, protections for people with pre-existing conditions, and insurance for young people. Now, conservative courts are cowardly following suit.

“The Republican Party should be ashamed and leaders in Congress must fight back against this reckless decision.”

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Rep. Nancy Pelosi, who is expected to become House speaker in January, vowed to fight what she called an “absurd ruling.” She said the House “will move swiftly to formally intervene in the appeals process to uphold the life-saving protections for people with pre-existing conditions and reject Republicans’ effort to destroy the Affordable Care Act.”

White House press secretary Sarah Huckabee Sanders issued a statement saying: “We expect this ruling will be appealed to the Supreme Court. Pending the appeal process, the law remains in place.”

(© Copyright 2018 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)