[glatt]

In an Obama administration, AG Holder said that in theory, the President has that authority within the borders of the USA. But it has never been exercised and would be highly unusual.

"As members of this Administration have previously indicated, the U.S. government has not carried out drone strikes in the United States and has no intention of doing so. As a policy matter, moreover, we reject the use of military force where well-established law enforcement authorities in this country provide the best means for incapacitating a terrorist threat. We have a long history of using the criminal justice system to incapacitate individuals located in our country who pose a threat to the United States and its interests abroad. Hundreds of individuals have been arrested and convicted of terrorism-related offenses in our federal courts.

"The question you have posed is therefore entirely hypothetical, unlikely to occur, and one we hope no President will ever have to confront. It is possible, I suppose, to imagine an extraordinary circumstance in which it would be necessary and appropriate for the President to authorize the military to use lethal force within the territory of the United States. For example, the President could conceivably have no choice but to authorize the military to use such force if necessary to protect the homeland in the circumstances of a catastrophic attack like the ones suffered on December 7, 1941, and September 11, 2001.

"Were such an emergency to arise, I would examine the particular facts and circumstances before advising the President on the scope of his authority."