If the precedent Mr. Obama has created is allowed to stand, future presidents who do not like what the Justice Department is telling them could simply cite the example of Mr. Obama’s war in Libya and instruct the White House counsel to organize a supportive “coalition of the willing” made up of the administration’s top lawyers. Even if just one or two agreed, this would be enough to push ahead and claim that the law was on the president’s side.

Allowing the trivialization of the War Powers Act to stand will open the way for even more blatant acts of presidential war-making in the decades ahead. Congress must confront the increasingly politicized methods White House lawyers are using to circumvent established law and stop them from transforming it into an infinitely malleable instrument of presidential power.