The constitution supposes, what the History of all Governments demonstrates, that the Executive is the branch of power most interested in war, and most prone to it. It has accordingly with studied care vested the question of war in the Legislature.And the first President to hold office under this system said this:
The Constitution vests the power of declaring war with Congress. Therefore no offensive expedition of importance can be undertaken until after they have deliberated upon the subject, and authorized such a measure.These are from Rand Paul's declaration of war against ISIS, which also rules out ground troops and limits the action to one year.
I do know this principle has been violated routinely in American history, but that doesn't make those violations a good idea.