She's talking out of her hat. The picture will look different after the president completes his presentation, and after the 16 hour Q&A.
More witnesses means days more sitting on their rumps listening to Schiff and Nadler.
And more days that Sanders, Warren, Klobuchar (and I cannot remember the other Senators running for the Dems) will not be on the campaign trail. Of course, that will probably only help their popularity.
Everyone seems to forget about Executive Privilege. I am not sure Bolton will ever testify and if he does he will be hamstrung. What Trump discusses with advisors is protected. Bolton will not even be allowed to discuss that conversation. So that begs the question if SCOTUS upheld Trumps EP what would that do to Bolton’s book.