When was the last time the United States formally declared war on another country?
Students in my American Law courses (at least the ones who have already completed the Introduction Course) know the answer to this, and understand that the U.S. Constitution is a bit confusing when it comes to the question of when the President can send the military oversees to engage in battle.
Article I of the Constitution clearly give the Congress the power to declare war, however the President is Commander-in-Chief of the military and charged with defending the interests of the country. Custom plays an enormous role in this question, and arguably it has become custom to allow the President to commit troops oversees without a formal declaration of war, as this recent post on the National Constitution Center's blog clearly illustrates.
