Here's the story, entitled somewhat blandly "Memo Cites Legal Basis for Killing U.S. Citizens in al Qaeda":
Obama administration lawyers have asserted that it would be lawful to kill a United States citizen if “an informed, high-level official” of the government decided that the target was a ranking figure in Al Qaeda who posed “an imminent threat of violent attack against the United States” and if his capture was not feasible, according to a 16-page document made public on Monday.
The unsigned and undated Justice Department “white paper,” obtained by NBC News, is the most detailed analysis yet to come into public view regarding the Obama legal team’s views about the lawfulness of killing, without a trial, an American citizen who executive branch officials decide is an operational leader of Al Qaeda or one of its allies.
If you go to the actual document, the key argument is, as you might suspect, that such killing is justified, despite the Constitutional right to due process (i.e., you can't be deprived of life without due process), because they balance the individual's right against unlawful deprivation of life against the interest of the state in national defense against imminent attack:
I'm not saying I don't agree with this reasoning. I'm also not saying that it's not a good legal argument. I'm just saying that this is the exact kind of argument and reasoning that the Left refused to grant credibility to throughout the eight years of Bush's Presidency. Instead they called him a murderer and a torturer and a war criminal and a Nazi.