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