AUSTIN, Texas — The latest push to scrap the Affordable Care Act once and for all pressed ahead Wednesday as Republican-controlled states asked a federal judge to finish what Congress started last year and bring the law that insures 20 million Americans to a halt.

A small group of protesters, some holding signs reading “Save the ACA,” shouted across the street from a Fort Worth, Texas, courthouse where former President Barack Obama’s health care law is again under attack. At issue are core principles of the law, including protections for people with pre-existing medical conditions and limits on how much older customers can be charged.

U.S. District Judge Reed O’Connor made no immediate ruling following a four-hour hearing. Twenty Republican-led states brought the lawsuit, arguing that the entire health care law was rendered unconstitutional after Congress repealed the individual mandate that required most Americans to buy insurance or risk a tax penalty.

“Texans and other Americans should be free again to make their own health care choices,” said Texas Attorney General Ken Paxton, a Republican who is leading the court challenge.

The case is the most high-profile legal challenge to “Obamacare” under President Trump, whose administration is not defending the law in court. But the Justice Department doesn’t want an immediate injunction suspending enforcement of the law.

Justice Department attorney Brett Shumate told the judge that any immediate injunction could create “a potential for chaos,” The Dallas Morning News and the Fort Worth Star-Telegram reported.

The arguments in Texas unfolded as senators in Washington pressed Supreme Court nominee Brett Kavanaugh, whose confirmation could swing the next major challenge to the health care law. Kavanaugh issued a 2011 opinion that some conservatives viewed as favorable to the individual mandate, but Democrats worry he will provide a key vote on the court against the law.