"While the president is the Commander in Chief, he does not control US foreign policy" 

Professor Peter Dean shares his Top 10 reasons AUKUS will survive the US election regardless of who wins.
#2: Congress controls foreign policy
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TRANSCRIPT
 Secondly, while the president is the Commander in Chief, he does not control US foreign policy because of the congressional system and the very big and very important role Congress has to play, particularly in funding initiatives. So we saw, as Mike said, when Trump threatened to pull troops out of South Korea, what did the Congress do?
Responded by putting amendments in the NDAA saying, you may want to do that, but we're not going to fund it. And given the very, very strong bipartisan support we've had in, around AUKUS in Congress, I would imagine that if there was some types of threats that Congress would move pretty quickly in a similar type of direction.