The logical next step in the war on the Islamic State is for Congress to declare it. That’s what President Obama seemed to suggest when he spoke to the nation Sunday about the slaughter at San Bernardino.

Seemed to suggest is the operative phrase. If Congress believes “as I do,” Mr. Obama said, that we are “at war” with the Islamic State, “it should go ahead and vote to authorize the continued use of military force against these terrorists.”

The President noted that for more than a year he’s been sending “thousands of airstrikes” against the enemy. “I think,” he said, “it’s time for Congress to vote to demonstrate that the American people are united, and committed, to this fight.”

Yet the authorization to use military force that Mr. Obama has offered to Congress is a nickel-plated version of a war declaration. It has more than four times as many words as were used to declare World War II, yet it fails to actually declare war.

The thing about a war resolution is that it ought to be a clarifying and unifying document. Five have been passed by Congress since America became a country. They are typically short and to the point and commit the nation to victory.

The resolution Congress passed after Pearl Harbor was 165 words long. It said simply that the “state of war between the United States and the Imperial Government of Japan which has thus been thrust upon the United States is hereby formally declared.”

It went on to say that the President was “hereby authorized and directed” to “employ the entire naval and military forces of the United States and the resources of the Government to carry on war against the Imperial Government of Japan.”

And then the famous words: “to bring the conflict to a successful termination, all the resources of the country are hereby pledged by the Congress of the United States.”

Period.

What a contrast with the timorous tissue Mr. Obama sent to Congress. It says nothing about a state of war being “declared.” Nor about the president being “directed” to use military force, merely authorized. Even before it gets to what he is authorized to do, the draft resolution reassures the enemy that the president will be “subject to limitations.”

Plus the resolution sets a time limit on the authorization to use military force. If Congress had tried such stunts with Franklin Roosevelt, he’d have flung his war cape at the solons and, so to speak, stalked out.

Imagine what the enemy must think when it’s the American commander-in-chief himself who is asking Congress to place these limits on his own war powers. No wonder the Islamic State’s thugs are strutting around like jackanapes from hell.

It may be that the Islamic State is a minor contraption compared to Imperial Japan, say, or Hitler’s Reich. But with nothing but some box-cutters, Islamist radicals killed more Americans on 9/11 than Tojo claimed at Pearl Harbor.

No doubt there are those who will suggest that a declaration of war is not required yet and is, in any event, over-reacting. But what does it take to awaken the sleeping American giant in the 21st century?

The clarifying and unifying nature of a proper war declaration is one of the phenomena that has been taught by history. On the eve of World War I, both the left and the right were famously in the peace camp.

How the debate raged — until Congress finally declared war. Then the agitators and second-guessers fell away. Many of them signed up — and even, in some cases, got the president to listen to their reformist pleas.

This happened famously in World War II, when the visionary labor leader A. Philip Randolph and his Brotherhood of Sleeping Car Porters forced FDR to integrate the war industries. The country came together from both directions.

It’s not my purpose to suggest our current crisis is a partisan problem. President Obama may be a Democrat, but Congress, at least for the moment, is Republican.

It’s hard to imagine we can defeat even the Islamic State if we are at war inside the Beltway.

This column first appeared in the New York Post.