The Dem standard was cooperation with a 4-year investigation into Presidential misconduct and finally testimony under oath by the President. That standard?We didn't create that standard--you people did. Just read any discussion here about Trump not giving them what they want.
Even if the DOJ is the right way to go, that doesn't preclude a President from asking a foreign leader if they can look into the matter. Trump never demanded it, never threatened anybody, just asked for a favor. A US President has the legal ability to look into any matter of possible corruption by a former representative.
No, a potential political opponent is not the same as a political opponent. And the commies never used the word "potential" once. So why did they use political opponent? Because that was the excuse they needed to impeach the President, because even they know that it's perfectly legal for a President to look into such things.
If Trump was interested in fighting corruption why was he insistent that the Ukrainians make the investigation public? That would give the subjects a heads up to start destroying evidence and would make no sense from an anti-corruption sense. Of course, if Trump was only interested in hurting Biden politically, the investigation had to be made public to be effective so then it would make sense.