As Gaddafi continues to slaughter civilians, America is fast approaching its own moment of truth. Despite its antiseptic label, imposing a "no-fly" zone is an act of war. As Secretary Gates explained last week, it "begins with an attack on Libya to destroy the air defenses." The president has gathered his advisers to decide how to proceed. But the Constitution gives Congress, not the president, the power "to declare war."
The president does have the constitutional power to repel attacks on the homeland, but nobody suggests that Gaddafi's assault on his domestic enemies is a threat to the United States. An attack on Libya's air defenses would be a war of choice, not self-defense.
No existing statute or treaty allows this action. Gaddafi isn't linked to Al Qaeda, so an attack against him isn't supported by the resolution authorizing force against terrorists involved in 9/11. If Obama goes it alone, he must return to Bush-era assertions that the president, as commander-in-chief, can unilaterally launch the nation into war.
Upon taking office, President Obama immediately withdrew opinions written by John Yoo and others making these extreme claims. And his Justice Department has refrained from asserting unilateral presidential power in the conduct of the wars Obama has inherited: Iraq, Afghanistan, and the drone attacks in Pakistan and Yemen.
But Libya would be Obama's war. If he acts unilaterally, he will be consolidating one of the worst aspects of the Bush era, and set a precedent for further abuses by future presidents.
There is still time to take the constitutional path. As Secretary of State Clinton recently explained, "no decisions have been made and for good reason. Because it is not at all clear yet what the situation demands." And Congress is likely to give the president its strong bipartisan support. John Kerry, chairman of the Senate Foreign Relations Committee, recently said that "we should be ready to implement [a no-fly zone] as necessary." Senator John McCain has gone further: "Don't tell me we can't do a no-fly zone over Tripoli."
The key question is not whether Congress will consent, but how it should limit its grant of authority. As Iraq shows, presidents can manipulate a poorly drafted Congressional authorization to escalate a war long after its original rationale has disappeared. It is one thing to approve a "no-fly zone"; quite another to authorize another decade-long effort at state-building once Gaddafi loses power.
To guard against mission creep, Congress should limit its no-fly resolution to a six month period. Conditions in Libya will be very different then, and it will be time for another round of debate. Congress can guarantee continuing oversight by stipulating that its current authorization expires on a fixed date. If the president wants the "no-fly" zone to continue, he will have to reopen the discussion, and convince Congress, and the American people, that the further use of force makes sense.
We are at a crossroads. President Obama can deal a death blow to our constitutional commitment to checks and balances in war-making. Or he can establish a precedent in constructive congressional engagement which will serve as a model for the foreign policy challenges of the twenty-first century.
Bruce Ackerman and Oona Hathaway are professors of law and political science at Yale. They expand on their sunset proposal in a recently published article in the Michigan Law Review.