Presidents invariably get Congressional approval for these actions. There is no Official Form for a declaration of War. Nor are all such actions suitable for such a declaration. Not all use of the military forces constitutes a "war" and there is no restriction on such uses within the Constitution.
I heard this loon opposing the war in Iraq and he did not base that opposition on not having a declaration of war. Congress clearly provided all the authority the President needed to do what he did. But Paul prefers to stick his head in the sand.
Article I, Section 8:
"The Congress shall have the power to...declare war..."
Odd, I do not see the word "make", which is what a preemptive strike is in action and nature.
Here is my concern. Since we have deemed it necessary to preemptively strike those we feel are a threat to us, should we be surprised when a nation preemptively strikes us because it feels that the United States is a threat to its sovereignty and safety? They would have precedent, thanks to the United States, to support their action.