The Dems strategy is crystal clear here. They rushed this through with only one thing in mind which Pelosi admitted today in a rare moment of honesty: tar Trump with the scarlet letter "I" so they can use it to influence the 2020 vote and further try to delegitimize his second term.
The theatrics today from Nadler claiming the Senate will be guilty of coverup if new witnesses aren't allowed, Schumer running around doing similar is nothing more than them passing the buck on a shoddy, rushed, weak and highly partisan bogus impeachment onto the Senate who they will blame when they don't get their way and when Trump is acquitted. They know the media will carry their water on this as well which is why the preemptive histrionics about the Senate also being on trial.