Well, collusion has a specific legal meaning which I dont think applies here. From the link I posted:
It's also important to point out that lack of precedent is not a disqualification for
establishing precedent. I agree that the analysis is correct because it merely claims that there is no precedent for prosecuting "collusion,"
in this way. Simply, it is very hard to prove and requires various piles of circumstantial evidence that all point to the same general narrative. It is those various piles of circumstantial evidence and shady contacts that seems to keep popping up, however, and as far as we know, Mueller has uncovered a substantial amount of it. "There is no law defining collusion in this way" is not the same as saying that it can't be prosecuted.
It is certainly likely that Trump and/or his admin and family, in various capacities, will find themselves on the wrong ends of various indictments due to crimes uncovered in this investigation. This doesn't necessarily mean that Mueller can't set a new precedent, depending on how thorough his investigation turns out to be, if he can paint a larger, cohesive narrative that connects all of their activities.
I personally think it more likely that Trump, through his own actions and those of his family, will be shown to be thoroughly compromised by the Russians. While not acting directly: "hey, help me win this election and I'll help you out!", the claim is that his vast financial interests in Russia and compromising/blackmail material controlled by Russian intelligence keeps him relatively trapped as what amounts to, in principal, a Russian "agent." His repeated behavior in abject defiance against US policy/Congressional sanctions to the
sole benefit of Russian interests is, to the least curious observer, rather alarming.