It is funny because it is the opposite actually. Former senates and presidents actually clashed over foreign policies, it is only in recent times that presidents were more or less left to decide. So, I guess there is a bit of projection going on here.

Congress has the power to declare war. The president being commander-in-chief does not mean he can do whatever he please with the U.S army as its own personal force. The president is meant to follow the constitution, even as commander. If the president ignores treaties and war declarations, I would argue the president is the one violating the separation of powers, and not congress by hypothetically enforcing the powers given to them by the constitution. By this logic, whoever controller the army should have absolute power, being commander-in-chief and all. I like how you slipped past my initial post by completely ignoring that the constitution grants congress influence over foreign policies by citing the president control over the armed forces as this unalienable right. Why have treaties then? Why have declaration of war? I think you might be slightly biased in your argument. The president was never the sole responsible for foreign policies, even though the executive branch had a lot of influence over those in recent times.

Article II section 2 of the constitution requires approval from the senate to ratify treaties, which is then up to the president to ratify and implement. Both branches of the government are supposed to work together to establish foreign policies, this is part of the check and balances. If you have sources interpreting article II section 2 differently I’d be curious to see.