Trump remains silent about Russia for three reasons.
If he were to acknowledge that the Russians interfered with the last Presidential election, in his mind, that would be publicly conceding the fact that his presidential victory was not legitimate. Something he knows is true.
At the same time he is considering the idea that because they did help him once then they probably will help him and the GOP again.
The third reason is that he has crawled so far up Vlad's colon to protect himself from the things Putin knows about his nefarious business deals, that he can no longer see the light of day.