Mitch wants a short trial but no one wants the short trial as badly as the democrats. They have already caved and are only putting up two articles of impeachment rather than the six or so that others want which would take them back into Mueller-ville, and run the trial out to about April. If Mitch gives em a short trial but makes them take stuff off the table to be able to make it short, then fine. I would take that deal. They know that ultimately Mitch still controls how long the trial will be. The big issue coming up is around is around what rules they are going to adopt for the trial. You can say well, duh, "we will just adopt the fed rules of evidence and evidence as in the past." Yeh, sounds simple, but that means that you are giving the president, as defendant, the right to call witnesses apart from what the senators may want. It's only fair right? So Trump will have to be managed in some way that keeps him from going full savage if they are making a backroom deal to not go wild with this witness thing on either side. The rules of fed criminal procedure do not automatically apply to an impeachment. The constitution leaves the rules up to the Senate, so they have to adopt some scheme or set of rules. Under the constitution, the president does not even have the right to be involved unless they agree to that and related rules. So their are bartering points there.