The Justice Department has a long tradition of defending statutes enacted by Congress, regardless of whether it supports the policies reflected in those laws.
But, Mr. Sessions said, this is “a rare case” in which the Justice Department has decided not to defend certain provisions of a law, because he could not find any “reasonable arguments” to support the constitutionality of the provisions.
Earlier on Thursday, three career lawyers at the Justice Department who had been working on the Texas case abruptly withdrew from the litigation.
Brett A. Shumate, a Trump administration political appointee in the civil division of the Justice Department who has played a leading role in defending the White House in a range of lawsuits, has joined the team handling the Texas case.
Even before the litigation is resolved, it could have more immediate effects on consumers’ wallets.
“The Justice Department’s brief creates another cloud of uncertainty for insurers, just as they’re filing proposed rates for 2019,” said Larry Levitt, a senior vice president of the Kaiser Family Foundation. “When insurance companies face uncertainty, they increase premiums.”
Xavier Becerra, the attorney general of California, said the Texas lawsuit was “based on a dubious legal claim.”
“We’re leading 16 attorneys general in court to stop Texas from destroying the Affordable Care Act” because “the Trump administration won’t defend the law of the land,” Mr. Becerra said.