The return of the imperial presidency

This statement from Julian Ku worries me because it's true:

There was a time when the debate over the use of force by the U.S. government focused almost exclusively on a domestic separation of powers conversation. U.S. legal scholars and elites would engage in debates about when and whether Congressional authorization is required before the President can use military force against U.S. enemies.  I think that this debate is basically over, thanks to the Obama Administration.