The prosecution's own witnesses have exonerated him. Sondland specifically said no quid pro quo. The others have no first hand knowledge, only their assumptions. They've testified he had every right to fire the ambassador, that he was concerned with corruption. The alleged victim has said there was no pressure. Hes been skeptical of foriegn aid going back to before he held the office and has held it up on numerous occasions.
The president released the transcript, the president is the one following the rule of law. The House has mocked the rule of law, charging obstruction of Congress because he dared take them to court. It is the Houses job to prove guilt, not the presidents to prove innocence.
They have alleged no actual crime. They have ignored an actual quid pro quo by one of their candidates.
Oh and there is no requirement for producing tax returns to hold the office.