United States Attorney General
The United States Attorney General heads the United States Department of Justice. He or she is appointed by the President, but the appointment must be confirmed by the Senate. The current Attorney General is Eric Holder.
Considered the chief law enforcement officer of the United States, the position is a powerful one, and the nominee is sometimes a political loyalist rather than a legal scholar, law enforcement professional, or judge. Part of the power of the office is that the Attorney General's signature can authorize certain investigative techniques comparable to those that might otherwise need a judicial warrant.
Second to the Attorney General is the Deputy Attorney General, and then the Solicitor General, who argues cases, for the United States government, before the Supreme Court.
The Attorney General has a dual role, as the chief law enforcement official, and as a Presidential appointee presumably supportive of Administration positions. It is not at all unprecedented that an Attorney General may conclude that a Presidential directive needs to be delayed, interpreted, or even refused. During the Nixon Administration, Attorney General Elliott Richardson resigned rather than carry out an order he believed to be illegal, i.e. Nixon's order to fire a Special Prosecutor (i.e., under the extant Special Prosecutor Act); the Deputy Attorney General,William Ruckelshaus, stepped up and then resigned as well.
During the George W. Bush Administration, John Ashcroft declined to agree to certain surveillance requests. He was hospitalized at the time, and had designated his deputy, James Comey, as Acting Attorney General. Comey also refused the order, brought to Ashcroft's hospital room by White House Chief of Staff Andrew Card and Counsel to the President Alberto Gonzales; Comey, at Mrs. Ashcroft's request, was present, along FBI agents sent by Director Robert Mueller, who had ordered that the FBI agents were to prevent Comey from being removed from the room. 
Eric Holder reopened an investigation into possible Central Intelligence Agency misconduct, started by Michael Mukasey in the Bush Administration, which Barack Obama had said he did not intend to reopen. Obama accepted Holder's decision.
- Charlie Savage (2007), Takeover: the Return of the American Presidency and the Subversion of American Democracy, Little, Brown and Company, ISBN 9780316118040, pp. 184-188