Multiple times during Donald Trump's second presidency, Congress has debated his military authority, first in Latin America and now the Middle East.
The latest test will come in the GOP-controlled House on Thursday after the Senate voted down a Democratic measure to limit Trump, at least theoretically, in the U.S.-Israeli war against Iran.
Like many predecessors, Trump claims broad, even unlimited power over U.S. forces. He approved boat strikes near
Venezuela, established a naval blockade and authorized a military operation to arrest and depose its leader, Nicolás Maduro — all arguable acts of war under international law. He made noise about additional action in Greenland and Latin America, before launching a sweeping bombing campaign in Iran.
Under the Constitution, the military reports to the president. But the document grants oversight roles to Congress. Trump says he won’t sign anything limiting his options — proof for some experts that control over a civilian-led military has skewed from its original design.
“The Constitution gives war powers to two different branches of government,” said military historian Peter Mansoor, an Ohio State University professor and retired U.S. Army colonel. “The pendulum has swung towards the executive,” he lamented, arguing that “the framers meant for Congress to be the most powerful branch.”
Here is a look at what the Constitution says and how U.S. war powers have played out.
Article I, which established Congress, states that lawmakers “shall have power ... to declare war.” Article II, which established the presidency, makes the chief executive the “commander in chief of the Army and Navy.” The Constitution also gives Congress authority over military budgets.
Congress has not declared an official state of war since World War II. Yet since 1945, U.S. service members have fought and died in full-scale conflicts in Korea, Vietnam, Iraq and Afghanistan, among other places.
In the Maduro mission, an Army pilot was injured, leading Trump to award him the Medal of Honor — recognition legally restricted to actions taken when fighting a foreign enemy. As of Wednesday, six U.S. service members had died in the Iran war.
During Senate debate last month on Venezuela, Sen. Rand Paul, R-Ky., mocked an “elaborate song and dance” and said it's “an absurdity” to argue that Trump's actions were anything other than waging war.
Sen. Tim Kaine, the Virginia Democrat who sponsored Venezuela and Iran war powers resolutions, said the latest version — which failed 47-53 — would prevent a presidential “end-run around the Constitution.”
Congress has declared war against 11 nations across across five wars. Three declarations came in the 19th century, two during World War I and six during World War II. Each time, the president formally asked Congress to act, citing some specific attack on the U.S. or another national interest.
President James K. Polk asked even for the Mexican War, which was principally about expanding U.S. territory.
Over the same span, Congress voted many times to authorize force without declaring war. Early measures were usually for specific naval actions defending U.S. commercial interests. Congress first took this route in 1798; it became a roadmap for the post-World War II era.
President Harry Truman won World War II under declarations issued while Franklin Roosevelt was president. Then, in 1950, the fledgling United Nations voted to act in Korea and asked member nations to assist.
Citing the U.N., Truman engaged U.S. troops in a so-called “police action" without seeking lawmakers' approval. Congress later that year approved the Defense Production Act to mobilize U.S. war capacity. It was an after-the-fact endorsement of Truman's decision, and the law remains a potential Pentagon tool.
Presidents from Dwight Eisenhower to Gerald Ford presided over what history remembers as the “Vietnam War,” though it was often called “the Vietnam conflict” as U.S. administrations expanded southeast Asia operations.
Lyndon Johnson persuaded Congress to pass the Gulf of Tonkin Resolution in 1964 and used that to accelerate U.S. involvement.
As U.S. deaths rose, the war grew unpopular, but Johnson — and then Richard Nixon — had broad authority from lawmakers. “Congress approves and supports the determination of the President, as Commander-in-Chief, to repel any armed attack against the forces of the United States and to prevent further aggression,” the 1964 resolution stated.
Congress repealed that measure in 1971, but Nixon did not withdraw.
Mansoor said war declarations don’t just define the start of a war. They also effectively require an official end — which triggers the Senate’s role in ratifying peace treaties. Sidestepping those legal bookends, Mansoor said, is “how you get in these forever wars.”
In 1973, as the U.S. limped toward its Vietnam exit, Congress passed the War Powers Resolution, intending to impose guardrails on presidents by requiring certain communication with lawmakers and allowing Congress to hold votes setting parameters for military action. That was the legislative trigger this year for failed Venezuela resolutions and the Iran resolutions.
In 2020, a Democratic-controlled House narrowly adopted a measure intended to curtail Trump’s powers against Iran at that point. But in practice the War Powers Resolution has not served as a functional check on executive power.
Ronald Reagan sent troops to Lebanon in 1982 as part of a multinational peacekeeping force. He did not cite the War Powers Resolution when notifying Congress and did not agree to congressional authorization until 1983 — after service members already had died.
In 1990, George H.W. Bush notified Congress under the War Powers Resolution that he'd dispatched troops to the Middle East after Iraq invaded Kuwait. Bush asked Congress for “support” — as opposed to “authorization” — only after securing U.N. backing for action by an international coalition led by U.S. forces. Congress authorized force in January 1991.
Bill Clinton deployed U.S. troops multiple times — to Somalia, Haiti, Rwanda, Bosnia and Herzegovina, Kosovo and Iraq. He asked Congress for appropriations but not explicit authorizations. When some lawmakers pressed Clinton to seek approval for strikes in Iraq in 1998, Clinton asserted his interpretation of presidential authority — not unlike Trump's arguments.
George W. Bush quickly mobilized the military after terrorist attacks on Sept. 11, 2001. He consulted quickly with Congress, resulting in a joint resolution authorizing sweeping action. It was unique because no specific country was targeted and it initially focused on al-Qaida. Congress nearly unanimously supported the measure but asked for reports every 60 days.
Mansoor, the military historian, noted that Bush used the vote to conduct antiterrorism efforts anywhere in the world. Bush returned to Congress in 2002, telling leaders he wanted authorization for action against Iraq.
What Congress passed for Bush had no effective end date. His successor, Barack Obama, inherited troops in Iraq and did not initially withdraw them. Afghanistan carried on through Obama's two terms and Trump's first presidency and into Joe Biden's term.
Biden withdrew U.S. troops from Afghanistan after it had become the longest U.S. war — never declared — in the nation's history.
