The U.S. Constitution grants Congress the sole authority to declare war, yet the ongoing conflict aimed at toppling Iran’s government has entered its fifth month without congressional approval. In fact, Congress recently voted with bipartisan majorities in both chambers to end the military action. This disconnect highlights how the constitutional war-making power intended for Congress has effectively shifted to the executive branch over time.

This transformation has unfolded in three broad phases. Initially, the Constitution allowed presidents to respond quickly to sudden attacks, while leaving broader decisions about war to Congress. However, as historian Arthur M. Schlesinger Jr. noted in his 1973 work “The Imperial Presidency,” the line between defensive and offensive wars became increasingly blurred. Presidents have repeatedly justified limited military interventions abroad as acts of self-defense, despite the Founders’ intent to distinguish such cases from wars of choice. For example, President James Monroe’s 1818 invasion of Spanish Florida was framed as a defensive action during conflict with the Seminole Indians.

This early ambiguity persists today. Former Secretary of State Condoleezza Rice recently argued that waiting for threats to become imminent could be dangerously imprudent, reflecting the challenge of establishing clear limits on presidential war powers. While the Constitution does not forbid preventive wars, it places the authority to decide on such engagements with Congress as the people's representatives.

The second phase of this shift came after World War II, when the United States emerged as a global superpower with military commitments worldwide. The prolonged rivalry with the Soviet Union complicated distinctions between wartime and peacetime, further consolidating military authority in the presidency. Scholars Jeh Johnson and Ethan P. Klaris have observed that the Korean War, fought without a formal declaration by Congress, exemplified this expanded executive role. The advent of rapid-strike nuclear weapons also necessitated swift decision-making, reinforcing presidential control over military actions.

Congress sought to restore its influence through the War Powers Resolution of 1973, which requires the president to obtain congressional approval for sustained military engagements. However, this statute has largely failed to curb executive war-making. It was only last month that Congress formally voted to end the Iran conflict, although President Donald Trump asserted afterward that he had halted the war only to resume it later following the collapse of a diplomatic agreement.

A third phase has solidified since the 2002 authorization for the Iraq War, illustrating congressional reluctance to approve military operations except under exceptional circumstances. Partisan polarization and Senate procedural hurdles also dissuade lawmakers from authorizing force, leaving presidents to act unilaterally. Since the Iraq War, there has been no formal congressional authorization for U.S. military actions in the Middle East, signaling a post-constitutional shift in U.S. foreign policy governance. Senate-approved treaties have given way to executive agreements, and congressional war powers have effectively become executive prerogatives.

Some analysts argue that this concentration of war power may enhance national security by enabling quicker responses to threats, given checking mechanisms such as public opinion, congressional funding authority, and political considerations—particularly presidential calculations about upcoming elections. Nonetheless, while the president’s unilateral authority has pragmatic benefits, it raises concerns about the erosion of representative democracy and the constitutional balance designed to prevent unilateral military commitments by any single branch of government.