I don't understand how the President can commit troops and military resources without the consent of Congress. Haven't all past U.S. Presidents gained approval from Congress before carrying out acts of war?
The idea is that the President, as Commander in Chief needs to have the ability to deploy US forces in case of sudden emergencies or to rapidly changing or short term opportunities where getting Congressional approval would hamper the response.
The actual power comes from the War Powers Act of 1973. It gives the President the power to deploy US forces, as long as they notify Congress within 48 hours. Those forces can remain in place for up to 60 days without Congressional approval.
Politically it was spurred on by the secret bombings in Cambodia and Laos. The reality being that the military may need to do things faster then Congress can react to, so at least they set a time limit and need to be notified but wont stop it from happening before hand.
Would recommend r/Ask_Politics for another view on it.