And honestly I'm not even sure why it still matters. There was more than enough cause for suspicion based entirely on Trump and his team's behavior w/r/t Russia leading up to the appointment of Mueller to warrant a full special counsel investigation, if for no other reason than to put to bed legitimate concerns about the allegiances of the President. And that's without considering the Helsinki fiasco, the secret meetings, the anti-NATO overtures, and God knows what else.
@ren hoek's argument that the reason for the investigation is somehow not valid and is sowing the seeds of suspicion is exactly backwards. The list of things unrelated to the investigation that have made many Americans reasonably and justifiably suspicious of Trump's motivations is a mile long; the investigation exists so that we can hopefully rid ourselves of those suspicions and replace them with fact as much as possible.