If they lose in 2020 they will all go down and they know it, your dealing with desperate people and Trump is the most desperate of all. It's a classic conspiracy case and they will all go away for life if they lose in 2020. Trump might go down over this shit though, he doesn't trust Mitch and shouldn't, Mitch will lose his senate majority if he acquits Trump, there is just too much evidence. The senate might not hear from Rudy and Lev, but the house will, along with a lot of other witnesses, Mitch knows this and will he will be tied to a completely out of control Trump right up to the election, if he acquits.
Just a simple majority would make the senate deliberations and vote a secret one.