That is well known. The FBI has been investigating that for some time based upon intelligence that was provided in, I think, July or August 2016.  That fact that Trump has lied and continues to lies about his Russian ties has only generated more suspicion. He is incapable of understanding that he's done this to himself, and that cheating in a presidential election is far and above cheating in private business deals.  It's a big, big deal and it doesn't just go away when you snap your fingers.  Much harder to hide your illicit activities when you have Unites Staes intelligence agencies looking into your sleazy behavior, not to mention intelligence agencies in forgein countries that you've alienated with your hateful, racist, nationalist rhetoric and outright insults.