There are precedents for what the Justice Department is doing, but not many. In 1946, in United States v. Lovett, the Supreme Court considered a case about a law withholding salaries from government officials said to be radicals. The executive branch complied with the law but told the Supreme Court it was unconstitutional. A lawyer representing Congress urged the court to uphold it, and the justices struck it down.

In 1996, the same year President Bill Clinton signed the Defense of Marriage Act into law, his Justice Department announced that it would enforce but not defend in court a law that required the military to discharge personnel infected with H.I.V.

"If the Congress chooses to defend this treatment of men and women in the military, it may do so," Jack Quinn, the White House counsel, said at the time. "But this administration will not." The law was repealed, making a court fight unnecessary.