If you'll settle for "something," He (mueller) already has. Trump's co-conspirator has already plead guilty. (It is a felony charge) Trump himself will have to wait until he's out of office (Coming soon, right after the "establishment" has no more use for him) to be indicted (probably) And then there is the illegality of his phoney "Foundation". (He's losing that civil case right now.*) Then rest assured Mueller has him on money laundering and tax evasion. He's just waiting. He can pass that on to New York, if he hasn't already. (Trump is powerless to stop it) So the only thing left is in what way did his campaign directly aid the Russian Hackers, if any. (information passed or money?) Meuller's having tea in Manafort's jail cell as I write this.

(Pence is stupid enough to pardon Trump, but ambitious and selfish enough that he might not. Trump is crapping in his pants right now, he is so nervous. Have you noticed how he is making a real effort to stick with the script someone has written for him. Trying to appear "presidential" and stop acting like a jackass leading up to the mid-term. You know why? It's because Jared told him if he didn't stop acting like a jerk they "weren't going to last in Washington". Ever since then he's been on a very tight rein. )
Have you noticed Trump isn't orange anymore? He's white as a sheet of paper. Well there is a reason.
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*Barbara Underwood is mean as a rattle snake, and shes got her fangs in him.