Sessions defended the unusual decision in a June 7 letter to Speaker of the House Paul Ryan.
They further cast the administration's brief, which was filed in federal court Thursday, as an "attack" on both the rule of law and the stability of the United States' health care system.
Texas and other Republican-led states are suing to strike down the entire Affordable Care Act, while California and other Democrat-led states want to protect the law, the AP reported. Last year, Congress repealed the tax associated with the penalty, effective 2019. They say the rest of the law is not able to be separated from the mandate, and therefore should also be overturned.
Congressional Republicans, who unsuccessfully sought to undo President Barack Obama's signature health care law throughout 2017, added language to the GOP tax bill that ended the controversial tax penalty for those who fail to obtain health care coverage.
"I find it impossible to believe that the many talented lawyers at the department could not come up with any arguments to defend the ACA's insurance market reforms, which have made such a difference to millions of Americans", Verrilli said.
"Justice Department attorneys don't withdraw from cases simply because the government is making an argument the lawyers think the courts should or would reject", he said. The DOJ in fact sided in large part with the states, arguing that the law's protections for people with pre-existing conditions should be invalidated. He said the department only refused to defend the pre-existing conditions provision as well as one forbidding insurers from charging people in the same community different rates based on gender, age, health status or other factors.
Despite the Justice Department position, the Health and Human Services Department has continued to apply the health law. Indeed, sign-up season for 2018 under the Trump administration resulted in only a slight enrollment drop-off from Obama's past year.
Insurers, meanwhile, warned that the administration's actions could rock the individual market and could lead to higher premiums, especially for those battling illnesses.