If the Republicans don’t put on a fair trial (where that’s defined for most people by what it looks like on TV), then he’s in double trouble. First, people will reject it, and second it will undercut all of the Republican lying propaganda about the “unfair Democrat star chamber witch hunt!” they have been ranting about for the past two months. Both of those hurt them with independents and people who want the investigation to proceed. Of course, McConnell may just ignore that in the hopes that people will forget by November, and try to put in a quickie trial that’s over before anyone can really get too involved in what is going on.
The play where they allow Republicans to call witnesses is worse for them, because in that case they will have to let Democrats call witnesses they couldn’t during the investigation…so we’ll get Mulvaney, Pompeo, Bolton, all of whom will have to testify under oath. And, all of whom will severely damage the Republican case, or else be caught out lying by the Democrats prosecuting the case. McConnell (and likely all the rest of them) know this, so they will do everything possible to avoid it…and, if they have to play fair, that feeds again into holding a quick trial with little evidence presentation.
I really do hope that Trump is able to force them into a big show trial, where he will figure his usual method of bluster and lies can carry the day. That will come up against a wall of hard evidence, and cross examination that destroys all of the conspiracy theories that Republicans are trying to get across. The desperation that Republicans will feel when that happens will be palpable, and I think that will turn the public as well…they will be able to tell the difference when everyone is watching every day.