If there happens to be witnesses, call Schiff (Will appeal) and also go to court over the 18th’s testimony. Then you subpoena Ciaramella and VINDMAN under the threat of perjury/prosecution.
I may have been unclear, but agree with that. A fact-finding forum without cross-examination, or oral arguments without ethical restraints can be inherently inefficient and exceedingly dangerous for the defendant.
However, Schiff is turning out to be a much better prosecutor than committee chairman and IMO will gain a vote for witnesses.
If so, it seems prudent to assume that Ciaramella's transcript either does, or will, carefully support the House argument, and Ciaramella survives a Senate deposition. IMO, the House also knows full well Bolton will support their position and views his role as not threatening. (The duration of legal entanglements for both will play right into the D's plans.)
In any event, the rhetorical question is what single supporting witness is available to the WH for response?