The collusion case is coming. I did not shift the focus. But, the case vs Donald Trump is that he likely obstructed the investigation (Collusion, Flynn, etc.) against OTHERS.
Moreover, and aside from all of the above, is the money trail. That is not necessarily criminal wrongdoing (money laundering) on Trump's part, but if he was financially "in bed" with the Russians, the optics/reality is that he was vulnerable to being compromised, thereby completing the circle re tax returns, campaign collusion, leaking top secret intelligence to the Russians, firing Comey, asking law enforcement to stand down, joking with the Russians about firing Comey . . . . . . and on and on.
This gets him impeached.
Try to keep up.