Obama hasn't just set a new precedent about killing Americans without due process. He has done so in a way that deliberately shields from public view the precise nature of the important precedent he has set. It's time for the president who promised to create "a White House that's more transparent and accountable than anything we've seen before" to release the DOJ memo.
I'm honestly ambivalent about the assassination of al-Awlaki. My bias is in favor of due process. On the other hand, it is not as though he was someone in the United States doing illegal things. If he really had--as has been asserted--an operational role in AQ, I think he could very reasonably be considered a legitimate military target first, and an American citizen second.
I think the question boils down to not--as Glen Greenwald and other civil libertarians whom I greatly respect have asserted--whether the president has the power to kill Americans abroad if they are engaged in terrorism, but rather if his citizenship is relevant to whether he was a legitimate target for the military prosecution of terrorists.
(By way of digression--this is a fine example of how messy things can get when the roles of the military and of law enforcement become muddled. But I'll leave that to another time.)
In any case, if the reasoning within the administration is so air-tight, then it ought to be made public.