Donald Trump (All General Trump Conversations Here) Isn't it the case, that when the House (as an entity) decided to begin impeachment proceedings, demands for evidence were valid? — Metaphysician Undercover
He... and the defense are trying to import civil rules to this...
not civil case.
There is no excuse for failing to honor a subpoena to testify as a witness on these matters of such national importance.
The relevant precedent(regarding the first article) is found during the Nixon administration. Trump has openly admitted to soliciting a foreign government to conduct an investigation on an American citizen, and he did so while refusing to follow the advice of the head of national security counsel. That American citizen just also happens to be a political opponent of Trump. Trump actually hired an outside counsel to publicly speak and/or act on his behalf about Ukrainian matters, long before this became public and people began resigning and whistle-blowing.
Trump got his side of the story out first.
There are several key witnesses all of whom had conversations with Trump and/or each other and all of their stories corroborated. Trump said "No quid pro quo" while continuing to hold back the funds and continuing to make a concerted attempt for Ukraine to do what Trump wanted, which - in and of itself - was for the Ukrainian government to interfere with an American presidential candidates life during election season.
That investigation has been performed and closed by the appropriate American institutions.