I tend to agree with Saz here. If Trump faces any sort of criminal proceedings (extremely unlikely), it will not be for "collusion," or treason, or anything else of the sort. It will be for money laundering or lying under oath or something along those lines.
It is very difficult to prove quid quo pro, especially when the President has a vested and authoritative interest in controlling foreign policy. And as far as I know, there is still no law requiring a President to give up interest or control over their private business prior to taking office, or showing their income tax statements, or proving that they are able to avoid financial conflicts of interest - which I think should be one of the primary legislative take-a-ways from this whole thing. While you're at it, Congressmen ought to have the same expectations, or at least be required to not vote on matters they will personally benefit from. No need for them to be making money on the side - the pay and pension is more than adequate for any patriot.
That said, the partisan origins and political nature of this investigation are irrelevant, as I now see it. This show will go on, and Trump has made himself brutally susceptible.