White House officials have a legal duty to testify before Congress.
Do they? Is that written down anywhere?
Executive Privilege isn't something Trump made up, nor even something Nixon made up. It's not only a long tradition. It's an important element of the doctrine of separation of powers, which is, as much as anything else, the foundation of a democratic society.
Congress wants something from the executive branch, so they issue a subpoena. If the President doesn't like the idea, he says no. Eventually, they end up in court, and if the Supreme Court rules against him, the President has to comply.
On Wednesday, I made a post scratching my head about all the "above the law" references, since Trump wasn't accused of breaking the law. Later that night, though, I listened to Stenny Hoyer's address, and I figured out what they meant. They think they are the law.
Well, if they can get 5 Supreme Court justices or 67 senators to agree with them, they'll be right.
Barr has testified multiple times to Congress Pompeo has testified 6 times before Congress and yet both refuse to testify about Ukraine. Why won't they testify about this? Could it be they did something wrong? Hmm

Only a damned fool would go to Congress from this administration to testify in this matter. This has "perjury trap" written all over it. If they do show up, they'll all demand immunity and they'll all have lawyers right next to them advising them to take the fifth on every question.
Does anyone actually think more testimony is needed? We know exactly what happened. Now decide if you think the President ought to be removed for it. If the people in charge want to call witnesses, then fine. They can call witnesses, but don't pretend that this is about finding out what happened. it's just about getting some good sound bites or, better yet, an indictment.
You seem to have made up your mind without the benefit of the witnesses. It seems like there must be plenty of evidence available. Sure, if you think witnesses would make a better show, call them, but all of you people wrapping this demand in some pretense of "fairness"....give it up.
The process is completely fair. You know what happened. The Congressmen and Senators have all the information they need. Witnesses won't add any more information or make anything more fair, whatever that means.
And no, it isn't like any other trial. Really. It isn't like any of them at all, because in a regular trial, the jury doesn't know what happened before they walk into the room. You have to present the facts before they can make up their minds. In this case, you have all already made up your minds, and you did so on the basis of the available evidence. So have the Senators. It's been front page news for months. It's all accessible. You need witnesses? Whatever for?