12AD.4.6a Special message to Congress on Mexican Relations, May 11, 1846

In the US Constitution, the power to “declare war” is explicitly granted to the legislative branch (Congress), as is the power to “raise and support armies.” However, the president is given the power as “Commander in Chief of the Army and Navy of the United States, and of the Militia of the several States, when called into the actual Service of the United States.” Since the exact powers of commander in chief are not fully defined, presidents have claimed executive power in times of war and crisis as implied powers of the Office of the President. In 1836, Texas declared its independence from Mexico, hoping to be annexed by the United States. Annexation occurred in 1845, which led to a war with Mexico. How did President James Polk argue that he had a right to declare war?

Texas declared its independence from Mexico in 1836, but Mexico did not accept its independence. Mexico threatened war if the United States annexed Texas, but Congress approved of the annexation, and in 1845 Texas became a state. President James Polk sent troops to the Texas–Mexico border purportedly to protect the new territory, but he did so without first consulting Congress. The actual boundaries were not clearly defined, and American troop presence heightened tensions with Mexico. When 16 soldiers were killed on the border of the Nueces River, President Polk went to Congress to ask for a declaration of war. In the US Constitution, the power to “declare war” is explicitly granted to the legislative branch (Congress), as is the power to “raise and support armies.” However, the president is given the power as “Commander in Chief of the Army and Navy of the United States, and of the Militia of the several States, when called into the actual Service of the United States.” Since the exact powers of commander in chief are not fully defined, presidents have claimed executive power in times of war and crisis as implied powers of the Office of the President. Presidents have used their commander-in-chief powers to create tribunals for prisoners, convene special courts to collect intelligence, deport noncitizens, and intern citizens who pose an alleged threat to national security. They have also used these powers to establish wartime agencies and programs to assist with the war effort. Sometimes these actions have been approved by Congress and sometimes they have not.

"Anticipating the possibility of a crisis like that which has arrived, instructions were given in August last, "as a precautionary measure" against invasion or threatened invasion, authorizing General Taylor, if the emergency required, to accept volunteers, not from Texas only, but from the States of Louisiana, Alabama, Mississippi, Tennessee, and Kentucky, and corresponding letters were addressed to the respective governors of those States. These instructions were repeated, and in January last, soon after the incorporation of "Texas into our Union of States," General Taylor was further "authorized by the President to make a requisition upon the executive of that State for such of its militia force as may be needed to repel invasion or to secure the country against apprehended invasion." On the 2d day of March he was again reminded, "in the event of the approach of any considerable Mexican force, promptly and efficiently to use the authority with which he was clothed to call to him such auxiliary force as he might need." War actually existing and our territory having been invaded, General Taylor, pursuant to authority vested in him by my direction, has called on the governor of Texas for four regiments of State troops, two to be mounted and two to serve on foot, and on the governor of Louisiana for four regiments of infantry to be sent to him as soon as practicable.

In further vindication of our rights and defense of our territory, I invoke the prompt action of Congress to recognize the existence of the war, and to place at the disposition of the Executive the means of prosecuting the war with vigor, and thus hastening the restoration of peace."