“[The North Korean] regime has signaled its contempt for its neighbors, for all members of the United Nations, and for minimum standards of acceptable international behavior," President Donald Trump said Tuesday morning. “All options are on the table.”

One option that should not be on the table is a “preventive” American military strike against North Korea without United Nations approval, public debate, and a congressional authorization.

If a foreign enemy attacks the U.S. or one of its allies first, or is preparing to do so imminently, the president can order an immediate retaliatory response. But if there’s no such initial attack, the commander in chief cannot decide for himself to take the nation to war. That decision is for Congress. The requirement is not a formality, and it’s not outdated. It’s a central requirement of our system, and for good reason.

Presidents have long chafed against limits on their military power, and each administration has sought ways around them. Evading Congress was dangerous when Barack Obama did it; it remains dangerous now that Donald Trump has pushed even farther than Obama. Under neither president did Congress act effectively to restrict the president’s authority. The world may soon reap the whirlwind that a broken political system has sown.

Georgetown law professor Martin Lederman (a former executive branch lawyer and a top authority on war powers) pointed out three weeks ago that an unapproved attack on North Korea would violate not only the U.S. Constitution but also U.S. law as set forth in a binding treaty and the fundamental charter of international law.

Begin with the Constitution. The framers and ratifiers rejected the British King’s “prerogative” to go to war (as recently as 2004, a Parliamentary report indicated that the government of Britain still has the power take the nation into war without parliamentary assent). At the Constitutional Convention, James Madison and Elbridge Gerry proposed language granting Congress the power to “declare war,” leaving, they said, “to the Executive the power to repel sudden attacks.”

Since the dawn of the Republic, presidents have been crowding the line between their command authority and Congress’s control of the military. Jefferson sent the Navy to fight the Barbary pirates, thus signaling that the new nation would defend itself on the seas. A century later, Theodore Roosevelt sent a naval squadron against the last Barbary pirate, Mulai Ahmed er Raisuni, in a show of force conveniently timed to highlight TR’s renomination.

Sometimes presidents sought approval beforehand, sometimes afterwards, and sometimes they ignored or defied Congress. In 1917, Woodrow Wilson sought authority to arm American merchant ships against German raiders (the U.S. was still at peace). A Senate filibuster killed the bill; Wilson armed the ships anyway.

By 1950, President Harry Truman felt empowered to commit the U.S. to full-scale “police action” in Korea without authorization; leaders of both parties acquiesced. Presidents Lyndon Johnson and Richard Nixon expanded the war in Southeast Asia and presidents expanded war-making authority by committing the U.S. to war in Southeast Asia while concealing the decision from the public. Congress responded with the War Powers Resolution of 1973, limiting presidential authority to commit U.S. forces into actual or imminent “hostilities.”

This, perhaps, is the true lesson of the drift toward executive power over war and peace: Congress doesn’t really want its war power back.

Presidents have pushed against the WPR as well. George W. Bush’s lawyers asserted that the power to initiate armed conflict was a decision solely entrusted to the president, and that Congress had no role to play. Nonetheless, when he took the nation to war in Iraq, Bush got authorization. When Obama authorized air strikes in Libya, his lawyers argued the raids were not “hostilities.”

Congress and the public scorned Obama when he actually asked for permission to intervene in Syria. This, perhaps, is the true lesson of the drift toward executive power over war and peace: Congress doesn’t really want its war power back.

Since becoming President, Donald Trump has threatened the President of Mexico with American troops; he has startled the Pentagon by announcing that he has a “military option” for Venezuela. Pushing past Obama’s scruples, Trump intervened in Syria on April 6; he has never bothered to explain to the nation or to Congress why, or what the nation’s objectives are.

Since then, Trump has proposed a new strategy in Afghanistan, but declined to explain what it is or how many more troops will be required. And his national security adviser, H.R. McMaster, told the nation that “preventive war” against North Korea may be in the offing.

This situation is dangerous. Trump has had a short course in executive effrontery and experienced nothing but reward. The wise heads of Washington, and the pundits of newspapers and cable TV, have scorned most of what he has done as president—but their praise for the Syrian intervention was rapturous. There’s little doubt that he believes he can do anything.

But he can’t, and Congress shouldn’t let him. As Georgetown’s Lederman points out, not only would a unilateral attack against North Korea violate the War Powers Act, it would also violate the United Nations Charter (which as a “treaty made ... under the authority of the United States” is, under the Constitution, “the Supreme Law of the Land”) and the text of the Constitution.

Begin with Article I. It explicitly grants Congress not simply the power “to declare war,” but the power to raise and support armies, to set rules for governing the armed forces, to control the training, arming, and discipline of state militias, and to decide how they can be called into federal service. What’s left over for the president is to command the military when it is lawfully engaged, in war or peace. That “commander in chief” power doesn’t sanction presidential wars.

Next, the U.N. Charter. This treaty, signed by many nations in 1945, ratified by the Senate, and enacted into federal law by the two houses of Congress, requires member states to settle disputes by diplomacy. If they cannot, they are required to seek advance authorization for military action from the Security Council. There’s an exception for self-defense “if an armed attack occurs”—not simply because a country might find it advantageous to attack first.

Finally, the War Powers Resolution. Many people believe the WPR “gives” the president power to commit U.S. troops abroad for up to 60 days. That’s a serious misreading.

The WPR says that the president may send U.S. forces into actual or imminent hostilities “only pursuant to (1) a declaration of war, (2) specific statutory authorization, or (3) a national emergency created by attack upon the United States, its territories or possessions, or its armed forces.” The 60-day provision is applicable only in the latter sudden attack case; the 60-day provision is a limit, not a license. After an emergency response, the president must seek authorization within 60 days; if Congress doesn’t grant it, the president is required to withdraw. “Nothing in this joint resolution,” the Resolution says emphatically, “shall be construed as granting any [new or independent] authority to the President with respect to the introduction of United States Armed Forces into [actual or imminent] hostilities.”

So far the score is, Congressional Authorization 3 (Article I, U.N. Charter, War Powers Resolution), Unilateral Power 1 (Truman in Korea).

But Truman acted only after South Korea—and American troops occupying it—had come under attack. He scrupulously obtained approval from the U.N. Security Council. I suspect even he would have blinked if his generals had come to him earlier, saying, “North Korea might attack, let’s go after them now without asking anybody.”

That Korean intervention went badly. Neither Truman nor the government as a whole explained to the nation or the world what America’s aims on the peninsula were. After the dazzling military success of early autumn 1950, U.S. and U.N. forces streamed north toward the Chinese border, ignoring diplomatic danger signs. China—fearing with some reason that the advancing allies might simply cross the Yalu and overthrow the Mao government—attacked suddenly, driving the combined U.N. forces back below the 38th parallel. It took more than two years of bloody stalemate to stabilize the two Koreas with a demilitarized zone between them. American public support for the war had long since collapsed.

The fighting eventually claimed nearly 37,000 American lives, more than 100,000 Chinese soldiers, and nearly 800,000 among the Korean people. In other words, Truman did badly in the Korean crisis, and one of his mistakes was not following the Constitution. That mistake helped produce the unstable peninsula that today threatens to spark the world’s first two-sided nuclear war.

There’s no reason to think that Donald Trump, acting alone, would do much better. The Constitution is there to make sure he gets help.

The administration might argue that an attack without warning would have a better chance of success. But the framers foreclosed that option, and their reasons were good ones.

If Trump takes the United States to war, he will no doubt demand national unity in support of the armed forces. And national unity is important in time of war. The Framers of the Constitution provided a way to unify the nation—let the people’s representatives, not one person, make the decision. Let there be a debate and a decision, not a series of tweets and cable-news panels.

The sagacious Lederman summarized the lesson: “No one individual, let alone the one presently in the West Wing, should be afforded the unilateral power to so radically transform the world.”