The power of Congress to declare war is the powey to initiate hostilities against another country that has not yet attacked us. It is NOT a required authorization to retaliate.
We can also be in a state of war with another country when they initiate hostilities against us, which is the situation with Iran.
President Trump, as Commander-in-Chief is well within his own power to wage that war. The War Powers Act does not apply here because there is no "chief" above the President whom he must check in with when we are already at war, as much as people like Rand want to micromanage him. Congress' only power is the Article I Section 8 power to fund the army for no longer than two years. If Congress disagrees with what the Commander-in-Chief is doing, they can always vote to not reauthorize funding for the military. They can also vote to not confirm any more officers in the military that President Trump might want or need.
But that's all they can do now, short of impeachment,but that would be seen as siding with the mullahs in Iran and supporting ongoing terrorism and the subjugation of women.
-PJ