“Attorney General Holder stated in a letter (archived link) to Sen. Paul dated March 4, 2013: ‘It is possible, I suppose, to imagine an extraordinary circumstance in which it would be necessary and appropriate under the Constitution and applicable laws of the United States for the President to authorize the military to use lethal force within the territory of the United States.’ ‘The U.S. Attorney General’s refusal to rule out the possibility of drone strikes on American citizens and on American soil is more than frightening – it is an affront the Constitutional due process rights of all Americans,’ Sen. Paul said.”
http://reason.com/blog/2013/03/06/sen-rand-paul-filibustering-john-brennan
