"If George Bush had done this, it would have been stopped." That's how MSNBC host Joe Scarborough characterized a Justice Department memo obtained by NBC News that outlines the Obama administration's legal rationale for killing American citizens suspected of helping al Qaeda prepare a terrorist attack on the United States. Critics say the 16-page document gives President Obama essentially unlimited powers to target U.S. citizens without trial, raising a host of ethical and constitutional questions about the administration's heavy reliance on drone missile attacks to enfeeble the terrorist network.

What criteria does the government need to meet to justify an attack on an American member of al Qaeda? According to the memo, an "informed, high-level official" within the government must determine that: 1) the individual in question poses "an imminent threat of violence attack against the United States"; 2) capture of the individual is "infeasible"; and 3) the attack is "conducted in a manner consistent with" the laws of war.

Upon even a cursory examination, however, these constraints are virtually meaningless. The government is not required to "have clear evidence that a specific attack on U.S. persons will take place in the immediate future." Furthermore, the feasibility of capture can be determined by several factors, including if it would simply be too risky for U.S. personnel to conduct a capture operation, or if a capture operation would imperil a "relevant window of opportunity." There are miles of space to maneuver within the so-called constraints.

The suspect could also be a member of "an associated force of al Qaeda," which presumably includes a wide spectrum of terrorist groups operating in Yemen, North Africa, Syria, and elsewhere.

Now, it's important to note that this memo is not some magic wand that the Obama administration waves around every time it wants to target a terrorist. The New York Times reports that the administration used a different memo in the assassination of Anwar al-Awlaki, an American-born member of an al Qaeda affiliate who was killed in Yemen. That memo and potentially others could have stricter, more specific criteria. However, the Awlaki memo and the newly released document both use the U.S.'s right to self-defense, the international laws of war, and Congress' authorization of "the use of all necessary and appropriate military force" against al Qaeda as the foundation for their legal frameworks.

Critics say it is far too much power to invest in the office of the president. "This is a profoundly disturbing document, and it's hard to believe that it was produced in a democracy built on a system of checks and balances," said the ACLU in a statement. "It summarizes in cold legal terms a stunning overreach of executive authority — the claimed power to declare Americans a threat and kill them far from a recognized battlefield and without any judicial involvement before or after the fact."

A more charitable view would be that this memo is part of a slow process to tack together a legal framework for a tactic that has become, for better or worse, a staple of modern warfare, which requires the government to confront perceived enemies that are small, isolated, and operate independent of nation-states. In 2010, Harold Koh — then the legal adviser of the State Department, and a fierce critic of the Bush administration's terrorist policies — was the first Obama official to publicly lay out the broad legal justifications for drone strikes. Attorney General Eric Holder last year said the Constitution's guarantee of due process does not necessarily entail a "judicial process" in situations in which national security is at stake. The hope in some quarters is that a more watertight legal framework will emerge, narrowing the use of drones to highly specific situations.

So far, though, the Obama administration hasn't produced that plan. Indeed, the administration hasn't voluntarily offered up anything to the public that would shed light on its decisions. That issue will presumably come up in the confirmation hearing later this week for John Brennan, the White House counterterrorism adviser who has been nominated to head the CIA.