That doesn't pass even the simplest examination. What if the thing that the democratically elected president promised to do was a coup?
See Napoleon 3, Hitler himself...
Your opinion is revealing, if you already think he has full power, then you agree it's a coup.
In both cases, the issue was the murder, not the democracy. It is important that we not blame democracy for the actions of evil men.
And then the head of state in the Weimar republic really was the chancellor, that's why Hitler could dismantle the republic.