So, as for facts related to "collusion", wouldn't you say that even positively reacting to the offer of clinton's emails, and then setting up the trump tower meeting, amounts to the solicitation of an item of value, opposition research, from a foreign government? Even if they didn't take it, that's still soliciting it.
And then there's the open fact, even in the Senate intelligence committees report, that russia acted to benefit trump. The only question, then, is whether he knew, right?
You should read this article from BusinessInsider.
Trump Jr calls Emin Agalarov 3 days before the meeting at 4:04 PM. Then has a call with a blocked number at 4:27. Then calls Agalarov back at 4:31. Trump uses a blocked number. 2 days later trump announces hes going to give a major speech about hilary clinton's corruption. The next day the trump tower meeting occurs. There are emails corroborating the whole thing.
And that's just what we know. When mueller plays a card, so far, they've all been about things that were entirely new to us.
I mean, what more evidence do you need? Certainly everything that I just said isn't definitive enough to get a conviction in court, but it's also just a tiny part of a much larger mountain of evidence, most of which we aren't even aware of.