Perhaps he heard rumblings, but what if he was protected and others did the dirty work? And he gets away scott free and because of that gets another term? Because it fits his personality to be used by others more intelligent than himself. Like Putin, McConnell, and other public and private influential Republicans who were happy to ride into power on Donald's coat tails.
It makes more sense, if they were smart, to keep Don out of the loop as much as possible. Because in his mind, he had the largest inauguration crowd in history. He won the popular vote. And he won the election WITHOUT needing Russia to win. So even if he does believe the intelligence agencies to some degree, his mind forms a mountain back into a mole hill, in order to keep prop up the delusion he has of himself as a 'success' that could have won anyways, so he'd rather just not hear about it. In his glorious mind, the Russia meddling story actually IS blown out of proportion and they were such a tiny influence compared to his awesome campaign.
I hope I'm wrong, that he was in on it from the beginning and helped coordinate it, and that is provable. But a part of me is worried that he was too stupid, and narcissistic and thus the operators that engineered this were able to do their work without even telling him the details. Because he didn't want to know the details. Not because it would have incriminated him, but for much more base reasons; he didn't want to ever believe that he needed any kind of help to defeat Hillary.