Eric Posner teaches at the University of Chicago Law School and is coauthor of The Executive Unbound: After the Madisonian Republic.

Harold Koh and John Yoo are two peas in a pod, except that Yoo is the right-wing pea and Koh is the left-wing pea. Yoo, a Justice Department lawyer during the Bush administration, interpreted “torture” narrowly in order to advance a constitutional agenda in which executive power has primacy. This interpretation permitted the Bush administration to use harsh interrogation tactics on suspected members of Al Qaeda. Koh, the legal adviser for Obama’s State Department, has now interpreted “hostilities” narrowly in order to advance a constitutional vision in which international norms and institutions play a role. Under Koh’s interpretation, Obama can keep troops in Libya despite apparently contrary provisions in the War Powers Act.

Many observers assumed that Koh and other lawyers appointed by Obama would repair the damage to the rule of law caused by Bush lawyers like Yoo—not follow in their path. Yet now, both Yoo and Koh have kicked up dust storms among law professors and other commentators who believe that the two lawyers distorted the meaning of a clear statute in an obvious way, and hence in defiance of Congress. These critics, however, are misguided....

Usually, the executive does not defy Congress outright; instead, it interprets ambiguous statutes aggressively in line with the executive’s view as to what should be done. But the executive has also staunchly maintained that its constitutional authority to conduct foreign relations cannot be overridden by Congress. It has typically chosen to advance narrow interpretations of the law rather than to insist that various statutes are unconstitutional, in order to avoid an explicit showdown with Congress over constitutional norms. The most famous example was Attorney General Robert Jackson’s opinion during World War II that the U.S. government could trade destroyers for leases on British bases, which was grounded in an extremely narrow and (to most lawyers) implausible interpretation of various laws that required the United States not to arm belligerents....