The US constitution specifically calls out treaties signed by the US (such as the UN Charta) as supreme law of the land. Article VI, the "Supremacy Clause".
Thus, US law, too, defers to international law.
Please at least read the legal framework you're so confidently misdescribing.
A law defines the nature of collective action in response to certain violations. Words on paper themselves are impotent. If there is no potential for enforcement, i.e. there is no counterfactual state of collective action, there is no law.
That sure is an attitude that explains why US soft power (and with that, Empire) has been crumbling at an unprecedented rate.
You might not care about the rules, but the rest of the world takes notice. This is how you break a world order carefully designed to further your own interests.
It's been the established president since the Korean War when the US began ignoring the constitutional provision that gave congress the power to declare war. Additional examples are the Vietnam War, Serbia, Afghanistan, Iraq I & II, the Libyan regime change, and the current Iran conflict, and there are plenty more. The written law still states that the president does not have this power, but the actual unwritten law has been that he can. And that is the only law that matters.
Yes, the US and not just the presidency. If it was just the presidency then he would have been impeached by congress for usurping their constitutional authority.
he was impeached (more than once cause he's a special kind of guy) and will be impeached again in 2029 :)
again, you are saying something is legal that is both clearly illegal and unconstitutional. you can say "it is illegal but we have no way to enforce since our congress and senate do not work for the people but are simple extension of a given political party in power" but you can't say that it is legal
You're going to have to specify a framework if you want to make statements about legality.