A confidential Justice Department memo concludes that the U.S. government can order the killing of American citizens if they are believed to be senior operational leaders" of al-Qaida or "an associated force" -- even if there is no intelligence indicating they are engaged in an active plot to attack the U.S. The 16-page memo ... provides new details about the legal reasoning behind one of the Obama administration's most secretive and controversial polices: its dramatically increased use of drone strikes against al-Qaida suspects abroad, including those aimed at American citizens. In March, Attorney General Eric Holder specifically endorsed the constitutionality of targeted killings of Americans, saying they could be justified if government officials determine the target poses "an imminent threat of violent attack." But the confidential Justice Department "white paper" introduces a ... "broader concept of imminence" than actual intelligence about any ongoing plot against the U.S. homeland. "The condition that an operational leader present an 'imminent' threat of violent attack against the United States does not require the United States to have clear evidence that a specific attack on U.S. persons and interests will take place in the immediate future," the memo states. Instead, it says, an "informed, high-level" official of the U.S. government may determine that the targeted American has been "recently" involved in "activities" posing a threat of a violent attack and "there is no evidence suggesting that he has renounced or abandoned such activities." The memo does not define "recently" or "activities."