The bottom line is the President has absolute power to use the Military to defend and protect the United States.
Congress can only limit him by refusing to fund any such action. Congress does have the sole power to declare War. But as noted they have not done so since WWII.
Historically Congress has not had the balls to de-fund such actions because they then become responsible for any bad things that occur from such removal of funding. They would rather the POTUS be the one hanging.
First, The military powers of the President have never been tested in the SCOTUS. Why? Because as long as it is a gray area Congress can scream and yell about it. But more importantly, no one wants to know the answer because if they win and the powers of POTUS are limited it can be dangerous for the Country.
Second, if they were to lose it and his powers were affirmed it would make POTUS even more powerful almost to dictatorship.
Third, no one wants to limit the powers of the POTUS because one day it will be their party in power and they don't want to lose that power.
That is the nutshell version of such matters.
Example, Obama broke the law when sending pallets of cash to Iran. But the POTUS has absolute power. That is just the way it is and rightly so. The power of POTUS can only be limited by the people, every four years. So Eff Nancy.