Last week, just before the Thanksgiving break, Senators Wyden, Udall and Heinrich sent Attorney General Eric Holder an important Thank You note.

In their Nov. 26 letter, the senators thanked the attorney general for providing the Senate Select Committee on Intelligence with access to the Justice Department’s opinions setting out the U.S. rationale for killing Americans via drone strikes.  (The United States has acknowledged killing four U.S. citizens using drones so far. Only one of those killings, it says, was intentional.) Although the letter doesn’t reveal the legal framework or specific facts the U.S. relied upon, the Senators say they believe “the decision to use lethal force against Anwar al-Aulaqui was a legitimate use of the authority granted to the President.”

But that’s only the beginning. The three senators go on to note that the U.S. government has failed to provide the same sort of information on any of the hundreds of other lethal drone strikes it has conducted outside of Afghanistan since 2009.  In fact, we still have no official explanation of whom the U.S. has secretly targeted, whom it has killed, and pursuant to which legal authorities.

The senators’ letter is yet another sign of growing pressure on the Obama administration to remedy that.  In just the last 6 weeks, two U.N. Special Rapporteurs have urged nations operating lethal drones to be more transparent about their use and their victims, warning that failing to do so could undermine international security.  And Human Rights Watch and Amnesty International both released reports in October detailing their investigations of killings conducted by the U.S. government in Yemen and in Pakistan, respectively, and strongly suggesting that some of the victims were not lawful targets.

Given that context, the three senators’ letter last week is particularly significant.  They write that, having seen at least some of the Justice Department’s legal memos themselves, they don’t believe the American public has been given adequate information about the killings carried out in their names. They conclude: “the limits and boundaries of the President’s power to authorize the deliberate killing of Americans need to be laid out with much greater specificity” so that “the American people can decide whether these authorities are subject to adequate limits and safeguards.”

The senators ask in particular for an explanation of “how much evidence [the Executive Branch] thinks the President needs to determine that a particular American is a legitimate target for military action”; how the Obama administration defines an “imminent threat,” and how exactly the administration concludes that a particular target’s capture is “infeasible” and that he therefore must be executed.  They also ask the attorney general to clarify whether the lethal strikes so far have been carried out pursuant to the 2001 Authorization for the Use of Military Force, or “based solely on the President’s own authorities.”

These are exactly the right questions to be asking – not only about the killing of Americans suspected of terrorist involvement, but about the targeting and killing of anyone in U.S. counterterrorism operations.

“In our view, the answers to these questions need to be shared not just with the congressional intelligence committees, but with the rest of Congress and the public as well.” Notwithstanding the oversight functions of the intelligence committees, the senators continue, “we do not believe that it is appropriate for the executive branch to rely on secret laws and standards . . . . As we see it, every American has a right to know when their government believes it is allowed to kill them.”

What the senators don’t say is that this applies to non-U.S. citizens as well.  Indeed, international law sets out strict limits on when the government of one nation can kill citizens of another one.  Those rules are different, depending on whether the state wielding the weapon is killing in the context of an actual armed conflict, or outside of one.  Whether regarding the killing of the four American citizens or the hundreds or thousands of others, the U.S. has never made clear which rules it is following, and how it is applying them.

Senators Wyden, Udall and Heinrich go on to make that point as well, adding that the “Executive Branch should be as open and transparent about the rules for targeted killing as possible.” After all, they continue, the United States is now setting the standards for 21st century warfare.

Moreover, when it comes to counterterrorism, it’s not only U.S. citizens who need to be convinced of the legitimacy of U.S. actions.  If U.S. counterterrorism operations are going to achieve their goal, they cannot be inciting more attacks against the United States and its interests.

As the senators conclude: “Increasing transparency about the rules that America follows when using military force would make the government more accountable to the public” and “increase America’s ability to hold other countries accountable for following international standards” as well.

Now let’s hope the attorney general heeds the senators’ call for more transparency – and can persuade President Obama to act on it.