I have to agree with Wasanelder. Let's say for a moment Mueller produces a tape of Trump saying to Putin, "Please hack Hillary's e-mails and have the Russian GRU throw the election" - I don't think even something that damning would matter. Because Republican's in the Senate would just hand wave it away.
They'd be on TV saying things like, "Well, everyone gets help from non-US actors in some way" and "Remember that one time Obama wore a tan suite at a White House briefing - that's the real crime we should be looking into" etc. Republican's wont even stand up for McCain when Trumps attacking him in the grave - do we really think they're going to stand up for the rule of law?
So long as Trump has his sycophants in Washington providing him cover nothing's going to stick to him. Maybe if he loses in 2020 he might be charged. But, the way things are going, I think he has a greater than 50% of being re-elected.