With friends and allies backing away from war with Syria, President Obama has been reduced to threatening unilateral military action—just enough so the administration won’t be “mocked,” said one unnamed official. But that’s also enough to violate the Constitution’s requirement for a congressional declaration of war.

The nation’s Founders feared just such a moment. John Jay pointed to the dubious motives that caused kings “to engage in wars not sanctified by justice or the voice and interests of his people.” So the Framers gave most military powers to Congress. Under Article 1, sec. 8 (11), “Congress shall have the power … to declare war.”

Future president James Madison explained the “fundamental doctrine of the Constitution that the power to declare war is fully and exclusively vested in the legislature.” The Founders did recognize that the president might have to respond to attack; however, this was a very limited grant of authority. George Mason favored “clogging rather than facilitating war.” James Wilson observed: “It will not be in the power of a single man, or a single body of men, to involve us in such distress; for the important power of declaring war is in the legislature at large.” Thomas Jefferson approved the “effectual check to the dog of war by transferring the power of letting him loose.”

No surprise, many presidents have pushed against the Constitution’s restrictions, unilaterally employing the military for different operations. However, most such deployments have been limited and temporary and many had colorable legislative authority.

Even strong presidents acknowledged the limits on their power. George Washington explained,“The Constitution vests the power of declaring war with Congress; therefore no offensive expedition of importance can be undertaken until after they shall have deliberated upon the subject, and authorized such a measure.” Similarly, said Dwight Eisenhower, “I am not going to order any troops into anything that can be interpreted as war, until Congress directs it.”

Barack Obama once agreed with his predecessors. In December 2007 candidate Obama acknowledged, “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.”

The Founders’ reasons apply even more today. War-making is the most extensive and most abused executive power.

Wrote James Madison: “Of all the enemies of true liberty, war is, perhaps, the most to be dreaded, because it comprises and develops the germ of every other. War is the parent of armies; from these proceed debts and taxes; and armies, and debts, and taxes are the known instrument for bringing the many under the domination of the few.”

So if President Obama wants to attack Syria, he must go to Congress. It doesn’t matter if he only envisions limited bombing raids. There is no plausible claim that Syria is preparing to attack America.

Nor are there constitutional exceptions for chemical weapons, bad dictators, or Mideast crises. President Obama must go to Congress.

The experience of Great Britain is instructive. Prime Minister David Cameron joined President Obama in demanding war. However, the House of Commons voted no. Asked whether he accepted parliament’s decision, the prime minister responded: “[I]t is clear to me that the British parliament, reflecting the views of the British people, does not want to see British military action. I get that and the government will act accordingly.”

As I point out in my new column for Forbes online:

It is equally clear that the American people do not want to see American military action and members of the U.S. Congress both desire to vote on war and likely would vote against war. There will be no United Nations Security Council resolution and the administration is being deserted by America’s European allies. When will the president “get that”?

If President Obama is intent on war, he must go to Congress. Going to war against Syria is not his decision to make.