That's what they've been doing so far. The last few testimony transcripts are hilarious! My favorite is Laura Cooper who testified that her knowledge of the Ukraine call stems from it's public release, and that she had not seen it prior to that date. She then testified that she had never spoken to the President or his chief of staff about the call. She then explained that her knowledge was the same as anyone who read the transcript for the first time.
Per her testimony, the only thing she knew about quid-pro-quo was what she heard from Bill Taylor, who said that he heard it from Tim Morrison, who Bill said heard it from Gordon Sondland, who Bill said heard it from the Ukraine President (who denied it).
It was like reading a comedy sketch! The dems called her as a witness! It's like credibility has no meaning to them!