President Madison had sent a message to…
June 1812 CE
After Madison's message, the House of Representatives had deliberated for four days behind closed doors before voting 79 to 49 (61%) in favor of the first declaration of war.
The Senate concurs in the declaration by a 19 to 13 (59%) vote in favor.
The conflict begins formally on June 18, 1812, when Madison signs the measure into law and proclaims it the next day.
This is the first time that the United States has declared war on another nation, and the Congressional vote is the closest vote to formally declare war in American history. (The Authorization for Use of Military Force Against Iraq Resolution of 1991, while not a formal declaration of war, will be a closer vote.)
None of the thirty-nine Federalists in Congress vote in favor of the war; critics of war will subsequently refer to it as "Mr. Madison's War."