My hope is that it can be proven that Trump and his camp directly colluded with the Russians in trying to interfere with the presidential election. Most things point towards that anyway, but I'm also fairly certain Trump has struck a personal deal with Russians that will enrich himself directly. Either of those things proven SHOULD be enough to get him thrown out/in jail, but the two of them together surely must do the trick.
Oh, the ex MI6 agent who wrote that uncorroborated dossier on Trump has resurfaced. Of course, no one in the Republican led branches seem too interested in hearing what he has to say, but there are plenty of things in that dossier which actually check out when investigated. Parts of the US media seem to be in the process of growing a backbone, so perhaps they will get to the bottom of this in the end.