NEW ORLEANS, July 9 (Reuters) - A federal appeals court panel grilled Democratic attorneys general on Tuesday about whether Obamacare violates the U.S. Constitution, as it weighs whether to uphold a Texas judges ruling striking down the landmark healthcare reform law.

The judges focused on whether the 2010 Affordable Care Act lost its justification after Republican President Donald Trump in 2017 signed a law that eliminated a tax penalty used to enforce the ACAs mandate that all Americans buy health insurance.

Republicans have repeatedly tried and failed to repeal Obamacare since its 2010 passage. The Justice Department would normally defend a federal law, but the Trump administration has declined to take that position against a challenge by 18 Republican-led states.

If you no longer have a tax, why isnt it unconstitutional? Judge Jennifer Elrod, who was appointed to the 5th Circuit Court of Appeals by Republican President GeorgeW. Bush, asked attorneys for the Democratic officials defending the law during a hearing in New Orleans.

A coalition of Democratic state attorneys general led by Californias Xavier Becerra stepped up to defend the law. The U.S. House of Representatives intervened after Democrats won control in Novembers elections during which many focused their campaigns on defending Obamacare.

A three-judge panel of the 5th U.S. Circuit Court of Appeals in New Orleans, is not expected to decide on Tuesday whether to overturn or uphold the ruling by a federal judge in Texas last year that the entire ACA was unconstitutional.

An appellate ruling declaring Obamacare unconstitutional could prompt an appeal to the U.S. Supreme Court, opening the door for the top court to take up the issue in the midst of the 2020 U.S. presidential election.

Obamacare, the signature domestic achievement of Trumps Democratic predecessor, Barack Obama , has been a political flashpoint since its passage.

Republican opponents call the law an unwarranted intervention by government in health insurance markets, while supporters say striking it down would threaten the healthcare of 20 million people who have gained insurance since its enactment.

In 2012, a divided U.S. Supreme Court upheld most of its provisions, including the individual mandate, which requires people to obtain insurance or pay a penalty.

The mandate compelled healthy people to buy insurance to offset sicker patients costs after Obamacare barred insurers from denying coverage to people with pre-existing conditions.

The Supreme Courts conservative majority argued that Congress could not constitutionally order people to buy insurance. But Chief Justice John Roberts joined the courts four liberal members to hold the mandate was a valid exercise of Congress tax power.

After Trump signed a tax bill passed by a Republican-led Congress that reduced the tax penalty to zero dollars, a coalition of Republican-led states headed by Texas sued, alleging the tax penaltys elimination rendered Obamacare unconstitutional.

U.S. District Judge Reed OConnor in Fort Worth, Texas, agreed in December 2018, saying the individual mandate was unconstitutional because it no longer triggered a tax.

OConnor, who was also nominated by George W. Bush, said that because Obamacare called the mandate essential, the entire law must be struck down.

(Reporting by Nate Raymond; Editing by Scott Malone, Jeffrey Benkoe, Susan Thomas and Bill Berkrot)