Can the CIA kill American citizens?

Apparently the answer to that question is ... "yes, we can"

The global war on terror, which led us to torture, Blackwater, drones, ..... now takes us to wondering about the legality of the CIA targeting an American citizen, not for capturing so that we might try the American in our courts but, instead, for assassination.  During Barack Obama's presidency?

I first came across this in Greenwald's post at Salon. Boy, that Greenwald is an excellent writer, with a clear logic.  Anyway, Greenwald writes:

The Washington Post's Dana Priest today reports 

that "U.S. military teams and intelligence agencies are deeply involved in secret joint operations with Yemeni troops who in the past six weeks have killed scores of people."   ...

But buried in Priest's article is her revelation that American citizens are now being placed on a secret "hit list" of people whom the President has personally authorized to be killed
After the Sept. 11 attacks, Bush gave the CIA, and later the military,authority to kill U.S. citizens abroad if strong evidence existed that an American was involved in organizing or carrying out terrorist actions against the United States or U.S. interests, military and intelligence officials said. . . .

The Obama administration has adopted the same stance. If a U.S. citizen joins al-Qaeda, "it doesn't really change anything from the standpoint of whether we can target them," a senior administration official said. "They are then part of the enemy."

I wonder if this is the change for which Obama won the presidency.
Greenwald further writes:

Barack Obama, like George Bush before him, has claimed the authority to order American citizens murdered based solely on the unverified, uncharged, unchecked claim that they are associated with Terrorism and pose "a continuing and imminent threat to U.S. persons and interests."  They're entitled to no charges, no trial, no ability to contest the accusations.  Amazingly, the Bush administration's policy of merely imprisoning foreign nationals (along with a couple of American citizens) without charges -- based solely on the President's claim that they were Terrorists -- produced intense controversy for years.  That, one will recall, was a grave assault on the Constitution.  Shouldn't Obama's policy of ordering American citizens assassinated without any due process or checks of any kind -- not imprisoned, but killed -- produce at least as much controversy?

The point is not to condone terrorism; but the fact that the President can simply order "off  with your head" as much as a king could do back in the 15th century--even though we are not a monarchy, and the Constitution establishes a due process .... Hmmm....
The LA Times adds:

Decisions to add names to the CIA target list are "all reviewed carefully, not just by policy people but by attorneys," said the second U.S. official. "Principles like necessity, proportionality, and the minimization of collateral damage -- to persons and property -- always apply."
The U.S. military, which has expanded its presence in Yemen, keeps a separate list of individuals to capture or kill. Awlaki is already on the military's list, which is maintained by the U.S. Joint Special Operations Command. Awlaki apparently survived a Dec. 24 airstrike conducted jointly by U.S. and Yemeni forces.
The CIA has also deployed more operatives and analysts to Yemen. CIA Deputy Director Stephen Kappes was in the country last month, just weeks before a Nigerian accused of training with Al Qaeda in Yemen boarded a jetliner bound for Detroit on Christmas Day.
From beginning to end, the CIA's process for carrying out Predator strikes is remarkably self-contained. Almost every key step takes place within the Langley, Va., campus, from proposing targets to piloting the remotely controlled planes.