Can Trump start a war with Iran without the approval of Congress?

Find Law - Can the President of the United States (POTUS) begin a military conflict without Congressional approval? As commander-in-chief of the U.S. military, how much control do they have? As you might expect, the answers aren't simple.

A President Is Not a King. The Founding Fathers wanted to avoid giving one person the authority to plunge the new nation into a war. While the office of the president was crafted with George Washington in mind, the creators of the Constitution realized that those who followed might lack his virtues and humility.

As such, it was left to Congress to declare war. This was considered well-established constitutional law until around 1950.

It is still unequivocally true that only Congress has the power to declare war. They've done so 11 times, the last time being during World War II.

It's understandable if you're scratching your head, remembering Korea, Vietnam, Afghanistan, and other conflicts that sure seemed like wars. While Congress has only declared war 11 times, it's also approved 108 "military operations" through resolutions.

This is where it gets complicated. A couple examples may help illustrate.

In 1950, President Harry Truman sidestepped Congress by going directly to the United Nations — then five years old — to authorize military action in North Korea. The U.N. did authorize military action, and Truman used U.S. troops to carry out the "police action."

In 1990, President George H.W. Bush believed a military response was required after Iraq invaded Kuwait. While ultimately Congress declared a joint resolution authorizing the deployment of troops, Bush maintained that he had the right to deploy troops regardless and would have done so even if it led to his impeachment. Bush felt it was vital to U.S. economic and security interests to protect Kuwait.

Ultimately, a Congressional resolution rendered the issue moot. However, it left a gray area regarding when a president can oversee the deployment of troops even without a declaration of war.

No president has ever made a formal declaration of war on their own.

As commander-in-chief of the U.S. military, the president makes all final military decisions during wartime...

Congress has also expanded and retracted the president's wartime powers. In 1941, the First War Powers Act gave President Franklin D. Roosevelt temporary control of many Congressional powers to enhance the efficiency of the war effort. These were repealed after the end of World War II.

The War Powers Resolution of 1973 (referred to as the War Powers Act) went in the other direction. It limits what the president can do with military forces if lacking Congressional approval. U.S. forces sent into combat are limited to 90 days without a Congressional resolution, 30 of which must be spent on their withdrawal.

While the War Powers Act limits prolonged engagements, it also grants the president the authority to "respond to attacks and other emergencies." This was the right that President Trump claimed in 2017 after ordering missile strikes against a military base in Syria without explicit Congressional approval....

Iran

On June 21, 2025, the U.S. military attacked three nuclear sites in Iran. Congress did not approve the action and has not declared war. Iran hadn't attacked any U.S. targets, but the Trump administration claimed that Iran's nuclear program meant that attacks were imminent.

The administration could try to frame any retaliatory strikes by Iran as justification to proceed without Congressional approval under the War Powers Act, at least for a limited time.

Congress could pass legislation limiting the president's war powers, but would need to gather enough support to override an almost certain veto from Trump. Representatives Ro Khanna and Thomas Massie submitted such a resolution in the House on June 17.