Why US Congress rarely stops presidents from waging war

The US Constitution grants Congress the exclusive authority to declare war, yet modern presidents have steadily claimed expansive powers to deploy military force on their own. 

Congress has largely allowed this, most recently when legislators failed to pass a resolution blocking President Donald Trump's military strikes against Iran.

The action has drawn sharp partisan disagreement over its legal basis, reports NPR. 

Democrat Senator Tim Kaine of Virginia argued that the founders had never intended military action without congressional debate and a formal vote, while Secretary of State Marco Rubio dismissed such concerns, telling reporters early this month that the administration had more than met its legal obligations.

The Constitution designates the president as commander in chief while reserving the war declaration power for Congress – a division that has proven far more complicated in practice than on paper.

How the Congress-president tension evolved

Columbia University law professor Matthew Waxman explains that this tension was minimal in the republic's early years, when presidents had to rely on Congress to fund any military campaigns. 

That arrangement held until Franklin Roosevelt sought a formal war declaration for World War II, the last time any president has done so.

America emerged from that war transformed: a nuclear-armed global superpower operating in a fundamentally different strategic environment. 

Yale law professor Oona Hathaway, who has advised the State Department across multiple administrations, notes that these changes reshaped the entire relationship between the branches.

The shift became starkly visible in 1950 when Harry Truman sent troops to Korea without congressional approval, launching what Waxman calls a "high-water mark of presidential unilateralism," a brutal three-year conflict fought without any formal authorisation. 

Lyndon Johnson did seek congressional backing before escalating in Vietnam in 1964, but Richard Nixon's secret bombing of Cambodia set off a backlash that produced the 1973 War Powers Resolution, Congress's effort to reclaim its constitutional role.

Hathaway says, "What Congress was really trying to do there was put itself back in the game, to assert its constitutional role."

What is the resolution?

The resolution requires advance consultation with Congress "in every possible instance," presidential notification within 48 hours of deploying forces into hostilities and withdrawal within 60 days, absent congressional authorisation. 

Congress also retains the ability to vote to end military action, subject to presidential veto. 

Hathaway cautions, however, that congressional inaction is not the same as approval – a point often misread as giving presidents a free pass for 60 days.

Presidents have generally followed the notification requirements and sought formal authorisation for the wars in Iraq and Afghanistan. The emergency exception has also been widely accepted. 

But they have repeatedly tested the boundaries by stretching definitions of terms like "hostilities" and "imminent threat," allowing Bill Clinton to strike Kosovo, Barack Obama to act in Libya, Trump to hit Syria and Biden to conduct operations in Yemen, all without congressional authorisation.

Current war

Hathaway and Waxman argue the current situation goes further still. 

A conflict touching more than a dozen countries in the Middle East, they say, is unmistakably a war in the constitutional sense and that Trump could have sought advance authorisation without surrendering the ability to act swiftly. 

They also flag potential violations of international law.

They say courts have largely stayed out of war powers disputes, leaving Congress as the only check, one it rarely chooses to exercise. 

As Waxman notes, drawing on James Madison's Federalist Papers framework of ambition checking ambition, presidents assert authority while Congress often finds it more convenient to stay on the sidelines and either praise or criticise outcomes after the fact. 

That calculation may shift if the current conflict drags on and the human and political costs begin to mount.