Congress has approved legislation that would prevent any president from withdrawing the United States from NATO without approval from the Senate or an Act of Congress. The measure, spearheaded by Sens. Tim Kaine (D-Va.) and Marco Rubio (R-Fla.), was included in the annual National Defense Authorization Act, which passed out of the House on Thursday and is expected to be signed by President Biden.
The Supreme Court has specifically made this point: The President “may not disregard limitations that Congress has, in proper exercise of its own war powers, placed on his powers.” Hamdan vs Rumsfeld (2006).
Just because the President is commander-in-chief does not mean he has plenary power over everything related to the military and it’s use.