A CONGRESSIONAL initiative to bolster President Obama’s legal authority to pursue the war against terrorist groups is generating surprising opposition.

The offending provision, introduced by House Armed Services Committee Chairman Howard P. “Buck ”McKeon (R-Calif.), asserts that the “United States is engaged in an armed conflict with al-Qaeda, the Taliban, and associated forces and that those entities continue to pose a threat to the United States and its citizens, both domestically and abroad.” As such, “the President has the authority to use all necessary and appropriate force during the current armed conflict with al-Qaeda, the Taliban, and associated forces pursuant to the Authorization for Use of Military Force.”

A score of liberal interest groups, including the American Civil Liberties Union and MoveOn.org, sent a letter to lawmakers to express concern that the provision could appear “to be stating that the United States is at war wherever terrorism suspects reside.”

We have one question: Where have they been for the past 10 years?

The United States has in fact been involved — as they ominously put it — in a “worldwide war” against terrorist groups intent on doing harm to the country, its allies and its interests. Two presidents from opposing parties have made clear that the United States would not stand idly by when other countries are unwilling or unable to ferret out the terrorists among them. The presidents were bolstered in their conclusions by the original Authorization for Use of Military Force (AUMF) and by international law, which recognizes a country’s inherent right to self-defense. The recent raid that resulted in the death of Osama bin Laden was a product of such an approach.

Yet a growing chorus of critics questions the legality of such operations against al-Qaeda and its cohorts, in part because 10 years have passed since the Sept. 11, 2001, strikes that gave rise to the original AUMF. Some point to Osama bin Laden’s death as further weakening the president’s authority to act under the AUMF. This is why a new reauthorization is necessary. The provision could be made to sunset after three to five years to address concerns that it is too open-ended; renewal would be subject to congressional approval.

None of the other terrorism-related proposals tucked into the defense bill by Mr. McKeon — including de facto restrictions on prosecuting certain terrorism suspects in federal courts — should be approved. The country needs a new legal structure to govern detentions, but Mr. McKeon’s proposal tramples on the president’s prerogatives and skimps on legal protections for detainees. But Congress should back the president’s lawful efforts to continue to battle terrorism and detain enemy combatants by endorsing a new AUMF.