I wondered why it never seemed to be an option, that Trump himself is asked to testify in the impeachment trial. The testimony of a defendant is after all a normal part of court proceedings in general, isn't it?
From the point of view of his defenders it makes sense, of course, because he is prone to unpredictable reactions and could possibly incriminate himself.
But why was this never discussed as a valid option?
In the U.S., Impeachment trials are "Quasi-Criminal Proceedings" (QCP) which are civil court cases which may result in criminal penalties. IN QCPs, the rights of the defendant must be protected as if the proceeding was criminal in nature and not civil (so if a wrongful death suit alleges criminal conduct was part of the reason for the death, than the defendent would be entitiled to similar rights as if it was a murder trial).
As such, Donald Trump's Fifth Amendment rights against compelled testimony against ones self would come into play as he is the "defendant" of the Impeachment Trial. Typically, compelled testimony can only be given if you are not under threat of such testimony criminally implicating you and it is not your trial (I.E. you can't be made to testify as an eyewitness to a murder if the reason you were a witness was because you were robbing the victims house and happened to be hiding in the closet when the victim was killed. In order to get the compelled testimony, you either have to be immune under "Double Jeopardy" OR by the prosecution deciding to not charge you in exchange for testimony). Otherwise, the only way for the defendant to testify in his/her own trial is if he/she decides he wants to do it... and most attorneys will advise against this as it does open up the defendant to cross examination by the prosecutor.
It's also important that there is no implications of one's guilt for refusing to testify in their own defense. It is the job of the Prosecution to prove the defendant did it no matter what the Defense does to counter his accusation.
Trump may be largely ignorant of the US political system, but he has decades of experience with the legal system, through bankruptcies, civil suits, and the like. Trump sees the legal system as a means to delay, harass, and confuse issues, with the ultimate goal of bleeding his opponent dry of time, money, and energy before any actual ruling occurs. Trump will always say that he is willing to give his side — because he always wants to appear as the 'good' person in the dispute — but he will never actually do it unless forced. Giving his testimony means giving the system enough material to draw conclusions and render judgments, which is precisely what Trump seeks to avoid.
For all of Trump's self-delusions and ignorances, he must be aware of how frequently his statements (to put it nicely) diverge from anything resembling observable fact. Even he would think twice about putting himself in a position where lying is actionable. It's one thing to disinform the public on public platforms like twitter; it is an entirely different kettle of fish to disinform sitting senators while under oath.
