"Obama supporters (and the conservatives who not coincidentally support him only in his Bush-replicating approach to the war on terror) who are dutifully insisting that the President not only has the right to order American citizens killed without due process, but to do so in total secrecy, on the ground that Awlaki is a Terrorist and Traitor, are embracing those accusations without having the slightest idea whether they're actually true. All they know is that Obama has issued these accusations, which is good enough for them. That's the authoritarian mind, by definition: if the Leader accuses a fellow citizen of something, then it's true -- no trial or any due process at all is needed and there is no need even for judicial review before the decreed sentence is meted out, even when the sentence is death.
For those reciting the "Awlaki-is-a-traitor" mantra, there's also the apparently irrelevant matter that Article III, Section 3 of the Constitution (the document which these same Obama supporters pretended to care about during the Bush years) provides that "No person shall be convicted of treason unless on the testimony of two witnesses to the same overt act, or on confession in open court." Treason is a crime that the Constitution specifically requires be proven with due process in court, not by unilateral presidential decree. And that's to say nothing of the fact that the same document -- the Constitution -- expressly forbids the deprivation of life "without due process of law."
To accept the word of the president - when he expressly offers no evidence and says it fact any evidence is legally blocked from being seen - on trust alone that someone is a terrorist is to ignore the fact that of of all the people held as terrorists at Gitmo over the last decade, over 70% were found to be not guilty of terrorism - the government's claims were found to be wrong when they had to stand up to even the most meager of judicial reviews - and released. The government has shown they are more often wrong than right when it comes to decreeing that someone is a terrorists, yet there is a considerable faction who, seemingly unaffected by external stimuli, continue to invest absolute trust and assume total accuracy every time the government makes that decree.
"If the president says he's a terrorist, he's a terrorist." Period, full stop, that's all you need. Revealingly, this level of childlike belief in the infallibility of the president only extends to when he wants to kill, imprison, or torture Muslims. When the president says something positive about the economy or health care or his new policy, we all correctly remain skeptical and want to see the evidence ourselves to determine its veracity. Regardless of our political biases, nearly everyone living has come to recognize that politicians often lie and are often wrong and what they say should not reflexively be taken at face value. For some reason though, for a considerable portion of people (authoritarians) this sensible skepticism does not apply to matters of defense, no matter how many times the facts eventually demonstrate the government is wrong as a matter of routine. These people are now willing to have someone murdered far from any battlefield or war zone and not engaged in any hostile actions, merely because the president in the tone of pure dictator or king, has decreed it. "No person shall be deprived of life, liberty or property without due process of law" be damned. Invoke the word "terrorism" and they'll line up behind whatever you say or do, even while clinging to being self-professed "Constitutionalists."
A simple question for those who see no problem in vesting this power in a single man without any outside checks, verification, adjudication, or accountability: If the President has the power to order American citizens killed with no due process, and to do so in such complete secrecy that no courts can even review his decisions, then what doesn't he have the power to do?