Declarations of war have never been a constitutional requirement for military action abroad.
Congress has created and funded a huge peacetime military that has substantial abilities to wage offensive operations, and it has not placed restrictions on the use of that military or the funds to support it, because it would rather let the president take the political risks in deciding on war. If Congress wanted to play a role in restricting war, it could - it simply does not want to. But we should not mistake a failure of political will for a violation of the Constitution.
Declarations of war have never been a constitutional requirement for military action abroad. The United States has used force abroad more than 130 times, but has only declared war five times - the War of 1812, the Mexican-American War, the Spanish-American War, and World Wars I and II.
