With the Obama administration planning what it describes as limited military strikes to punish Syria for its alleged use of chemical weapons, public discussion over the legality of U.S. action has addressed mainly questions of international law. Commentators debate whether the United States may take action without authorization from the U.N. Security Council. That is an important question. But debate within the United States typically ignores a separate, more fundamental question: Does the Constitution authorize President Obama to take military action against Syria without congressional approval?

When he was running for president in 2007, Obama, a former constitutional law professor, told reporter Charlie Savage that “the president does not have power under the Constitution to unilaterally authorize a military attack in a situation that does not involve stopping an actual or imminent threat to the nation.” That was an accurate description of U.S. law.

The drafters of the Constitution assigned Congress the power to declare war. Records from the constitutional convention in Philadelphia show the framers recognized that, in an emergency, the president could act unilaterally to repel a sudden attack against the United States. This was a consensus view. Even Alexander Hamilton, who had the broadest view of executive power, acknowledged that under the Constitution, “it is the peculiar and exclusive province of Congress, when the nation is at peace, to change that state into a state of war; … it belongs to Congress only, to go to war.”

As Louis Fisher of the Constitution Project concludes: “The framers placed in Congress the authority to initiate war because they believed that executives, in their search for fame and personal glory, had a natural appetite for war and military initiatives, all of which inflicted heavy costs on the interests and liberties of their people.”

As candidate Obama recognized in 2007, the president needs congressional authorization for a military attack that is not related to an actual or imminent threat to the United States. What is happening in Syria is an ongoing atrocity. Tens of thousands of people have been killed — some, it appears, by the Bashar Assad government’s use of chemical weapons. This is a moral outrage. But it is not a direct threat to the United States, and the Obama administration does not suggest otherwise.

In order to find domestic authority for its actions, the administration would probably cite the War Powers Resolution of 1973, which seems to provide authority for the president to take the nation to war for up to 60 days or, in some circumstances, 90 days, without congressional approval as long as the president reports on his actions to Congress. The problem, however, is that the resolution — a legislative act — cannot trump the Constitution.

Since 1973, presidents and advocates of broad presidential power have argued that the resolution unconstitutionally limits the president’s ability to use military force. They are right that it is unconstitutional, but their reasoning is backward. The resolution is unconstitutional because it gives the president too much power by assigning some of Congress’ war power to the president. It does not provide legitimate authority for the Obama administration to order military action in Syria.

It is true that presidents — including Obama in the case of Libya two years ago — have ordered military action without congressional approval. The most notorious case is President Truman’s unilateral decision to send U.S. troops to the Korean peninsula. But past presidential practice cannot amend the Constitution.

None of this means the U.S. government is powerless to act. The Constitution provides a procedure: Congress can authorize the use of military force. If Obama believes military action in Syria is in the national interest, he should make his case to Congress and the public, as more than 100 lawmakers have urged.

Despite the horror of what is happening in Syria, history teaches that there is good reason for Congress and the public to ask questions. Military operations intended to be limited may turn into protracted action. Military strikes intended to be “surgical” may affect civilians. Military action against the abhorrent Assad regime may unintentionally help opponents of it, some of whom have ties to terrorist groups. As candidate Obama would have recognized in 2007, that is exactly why unilateral presidential action would be neither wise nor constitutional.

Chris Edelson is an assistant professor of government in American University’s School of Public Affairs, where he teaches classes on the Constitution and presidential power. He is the author of the forthcoming book, “Emergency Presidential Power: From the Drafting of the Constitution to the War on Terror.”