You're going to have to specify a framework if you want to make statements about legality.
Thus, US law, too, defers to international law.
Please at least read the legal framework you're so confidently misdescribing.
That's obviously not how things work. If you don't obey the law, you are a criminal. That's the whole point of laws.
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.
First, not US but Presidency and second, breaking Constitution is not very legal last time I checked but I could be wrong... /s
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
Well you can say the same about Putin then. All nice and dandy
The problem is: over time the US grew so powerful, that the definition of "war" became blurry. "No, we are not at war, our soldiers are just dropping bombs on Iran for fun and profit".
EDIT: Another problem, of course, is that current member of Congress have no balls to stand up to Trump and reclaim their constitutional powers.