Acting on President Trump’s orders, the U.S. military conducted a strike early Sunday morning against three Iranian nuclear facilities. Few knew of the strikes in advance. Mr. Trump did not seek advance approval from Congress or the U.N. Security Council, as required by law. The unlawful strikes have thus laid bare the dangerous absence of any effective legal constraints — whether domestic or international — on the decision of the American president to use deadly force anywhere in the world.

It has become almost quaint to observe that the Constitution gives Congress, not the president, the power to declare war. Yes, the president is commander in chief of the military, but he is obligated to seek authorization from Congress before he initiates a war. The 1973 War Powers Resolution does not change this. Enacted in response to President Richard Nixon’s secret bombing campaign in Cambodia, that legislation is meant to prevent a president from launching illegal wars by legally requiring the president to seek approval of Congress before introducing U.S. armed forces “into hostilities or into situations where imminent involvement in hostilities is clearly indicated by the circumstances.” The only case in which the president is not required to seek the advance approval of Congress is when the United States has been attacked and he must act quickly to protect the country.

That was not true when it came to Iran. Quite the opposite. In a speech after the attacks, Mr. Trump pointed noted that Iran had been making threats against the United States for “40 years.” Nothing in what he or Secretary of Defense Pete Hegseth has subsequently said points to an urgent threat to America that prevented the president from seeking Congress’s consent before unleashing deadly force that could provoke retaliation against the United States and U.S. forces in the region. (And indeed, such a retaliation appears to have just taken place, as Iran fired missiles at a U.S. base in Qatar.) Nor can these strikes be shoehorned into the existing congressional authorizations for the use of force — one in 2001 against those responsible for the Sept. 11 attacks and another in 2002 against Iraq under Saddam Hussein. The president has thus claimed for himself power that the Constitution expressly gives to Congress.

Just as the president is legally bound to seek authorization from Congress before launching a war, so too is he required to seek authorization from the United Nations Security Council. In the wake of World War II, the United States designed and championed a global system where the use of coercive authority by any state against another was subject to collective checks. The United Nations Charter provides that signatory states must “refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state.”

This prohibition on the unilateral resort to force is the foundational principle of the postwar legal order. Only if the Security Council votes to authorize a war — or where a state is the subject of an “armed attack” — may a state that has ratified the U.N. Charter resort to force against another state. Yes, the requirement of gaining support from the Security Council is an obstacle, but it is an obstacle to Russia and China as much as it is to the United States. The requirement to seek and obtain Security Council authorization before using force, moreover, gives the United States extraordinary power: The United States holds one of five permanent seats on the Security Council and, with it, has a veto over any decision to authorize the use of force. While no legal system is perfect — and this one is no exception, as today’s global conflicts show — the U.N. Charter has nevertheless helped produce the most peaceful and prosperous era the world has ever seen.

Donald Trump has now fully embraced the so-called Bush doctrine, a foreign policy stance that holds that the United States can use force pre-emptively against a perceived threat — to itself or others. This was the key legal basis for the disastrous 2003 war in Iraq, held up as necessary to prevent the use of weapons of mass destruction — weapons that, it turned out, did not exist. Even then, President George W. Bush at least engaged with the Security Council and sought and won authorization from Congress before he launched that war.