I had a lengthy chat yesterday with a good friend who’s involved with the ACLU. The topic at hand: the strike on al Qaeda’s Anwar al-Awlaki late last week.

As one might assume, my friend, who’s generally quite sympathetic to the Obama presidency, wasn’t at all pleased with the developments — when the American government knowingly kills an American citizen without due process, there’s a problem. I noted some contextual details — Awlaki left the country, became an al Qaeda leader, allegedly played some role in several terrorist plots, and practical considerations apparently made apprehension impossible — which might make the picture slightly murkier. Might. Maybe. I think.

But of all the concerns raised about the U.S. killing Awlaki, the one that struck me as most persuasive has to do with checks and balances: this kind of power shouldn’t rest in the hands of one person sitting in the Oval Office. There must always be checks and balances, layers of oversight and accountability.

Kevin Drum had a good item on this over the weekend.

As it happens, I don’t think the Awlaki precedent means that President Obama is going to go hog wild and start mowing down Americans overseas. I don’t think that President Rick Perry would, either. But there are good and sound reasons that presidents are constrained in their ability to unilaterally kill U.S. citizens, regardless of where they live, and we allow these bright lines to be dimmed at our peril.

Unfortunately, the war on terror has made poltroons out of every branch of government. The president hides behind the post-9/11 AUMF, using it as a shield to justify any action as long as it’s plausibly targeted at al-Qaeda or something al-Qaeda-ish. Congress, which ought to pass a law that specifically spells out due process in cases like this, cowers in its chambers and declines to assert itself. And the courts, as usual, throw up their hands whenever they hear the talismanic word “war” and declare themselves to have no responsibility.

I realize that when it comes to national security and the use of military force, there’s one commander in chief, and a variety of weighty decisions will rest on his or her judgment. But there are, and should be, limits. There must be.

I can’t speak with any authority as to whether the Awlaki killing falls outside those limits. Glenn Greenwald and others made a strong case on Friday that it does, and they may well be right.

What I’d like to see is the legislative branch do what it’s supposed to do: draw clear lines. In this case, the executive branch presented a rather bold proposition: it saw the evidence, it saw the intelligence, and it made a judgment call about a military strike. It’s not inconceivable to me that the strike was justified based on limited national security options.

But when there are questions about the scope of presidential power, our system works best when they’re answered, not ignored. In this case, as a political matter, I imagine many in Congress will be pleased that the administration killed a prominent figure in al Qaeda, but many in Congress should at least be prepared to explore what transpired, and consider whether this much power should rest in the hands of one individual.

If the legislative branch lets this go without so much as a hearing, the scope of presidential power will grow in unhealthy ways. It’s never surprising when the executive claims expansive authority over national security — administrations have been doing this for generations — but it is surprising when Congress simply washes its hands of the subject.

If President Obama blurred the lines last week — and by all indications, he did — it’s up to lawmakers to make them clearer. They have a responsibility to do so quickly.

Steve Benen

Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.