Apparently, the Obama administration isn’t saying even though they have repeatedly been asked.  From Greenwald:

The Justice Department “white paper” purporting to authorize Obama’s power to extrajudicially execute US citizens was leaked three weeks ago. Since then, the administration – including the president himself and his nominee to lead the CIA, John Brennan – has been repeatedly asked whether this authority extends to US soil, i.e., whether the president has the right to execute US citizens on US soil without charges. In each instance, they have refused to answer.

It seems pretty obvious that the Obama administration is unlikely to agree to a restriction on his power to use drones as he sees fit without a knock-down-drag-out fight and it is equally unlikely that a majority in Congress will put forth that degree of resistance.  while the democrats would be outraged by such a position from a republican president, they aren’t so bothered when the president is from their own party.  Another case of, “It’s okay when our guy does it.”