A U.S. president is not supposed to be able to start a war without authorization from Congress. But the last several decades have blurred the line regarding what military action a president can take without first obtaining Congressional approval.
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.
Congressional Action and Wartime Powers
As commander-in-chief of the U.S. military, the president makes all final military decisions during wartime. This includes the following:
- Deploying troops
- Invading hostile countries
- Sending spies into enemy territory
- Using nuclear weapons
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.
More leeway was given to the Executive Branch through 2001's Authorization for the Use of Military Force (AUMF). This joint resolution by Congress allowed President George W. Bush to attack any nation or group he considered responsible for the terrorist attacks on 9/11. This was also used by President Barack Obama in 2014 against the Islamic State.
What Does This Mean for Iran, Greenland, and the Panama Canal?
Earlier this year, the Trump administration seemed to focus mainly on Greenland and the Panama Canal as potential sites for military action. However, recent events in Iran have brought these questions back to the forefront in a very real way.
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.
Greenland
Greenland is an autonomous territory of the Kingdom of Denmark. It became a Danish state in 1814 and was fully integrated as an amt (county) in 1953. In 1979, Greenland was granted home rule.
The U.S. has long had a friendly relationship with Greenland. It established military bases in Greenland during World War II and still maintains the rent-free Pituffik Space Base, formerly known as Thule Air Base. The U.S. made an offer to buy Greenland from Denmark in 1946 for $100 million. The offer was not accepted.
Denmark is a NATO member. It's difficult, if not impossible, to find legitimacy for the U.S.'s claims about attacking Greenland. While Congress could declare war at any time for any reason, doing so against long-time allies for economic reasons would be unpopular, to say the least.
The Panama Canal
Originally started by French interests, the Panama Canal connects the Pacific Ocean and the Caribbean Sea. The ingenious 51-mile-long system of locks has been in service since 1914. This includes expansions made to allow larger ships to pass through.
The U.S. took over construction in 1904 and was in control of the Canal until 1979, when it entered into a partnership with Panama. Full control of the canal was passed to Panama in 1999.
Is This War?
Despite President Trump's adamant assertions that the U.S. would be justified in attacking targets in all these countries, the U.S. Constitution could limit his ambitions, particularly when it comes to endangering U.S. troops.
However, the second Trump administration has been defined by taking action first and arguing the legality of those actions later.
By the letter of the law, Congressional approval is required to start a war, but AUMFs and other workarounds have become a standard practice for U.S. presidents. How the rest of the world reacts to the U.S. attacking a fellow member of the United Nations is yet to be seen.
As of June 23, Iran has not issued a formal declaration of war, although they have begun retaliating against U.S. bases.
Related Resources
- Implied Executive Powers (FindLaw and the U.S. Constitution)
- What Is the War Powers Act? (FindLaw's Law and Daily Life)
- The Panama Canal and the Torrijos-Carter Treaty (U.S. State Department)
