A simpler way to frame this that hundreds of people have now pointed out, which has the helpful property of extracting the scary alien new "drones"† from the equation: the authority Holder is claiming for the administration is the same as the one that would allow them to down a jetliner hurtling towards the Sears Tower: an intervention only available to the military.
There were good questions available to Rand Paul before he decided to prematurely declare victory over common sense. Two I can come up with:
* Does the administration claim the right to use military resources to attack US citizens on US soil if compelling evidence exists that they are al Qaeda terrorist when no specific evidence exists that such a person plans to imminently attack the US? Can the US use an airstrike against an al Qaeda terrorist who is a US citizen simply to keep them from "getting away"?
* Does the administration claim the right to use airstrikes against al Qaeda terrorists of any nationality when a reasonable person could infer a likelihood that such a strike would cause harm to Americans in the vicinity of the strike?
There are more good questions, I'm sure. "Could there ever be a case when..." is literally the "ticking time bomb" question; the dumbest of all questions.
† Scared kids in combat boots with M16s have done far more damage to innocent lives, both at home and abroad, than drones will ever do; drones are often a way of affecting concern for the lives of people 'like us' while ignoring the safety of civilians and servicemembers on the ground.
†† "What stupid question?" This one: http://news.ycombinator.com/item?id=5335285