Levin has said he would vote for Trump if he gets the nomination.
He has also said that he personally likes Trump. Apparently, that is not enough to satisfy Trump’s base. Anything short of an endorsement from every public figure is an attack to them. It is also apparent that Trump’s base is full of short term strategists. Insulting guys like Levin during the primaries may make conservative talk show hosts much less enthusiastic about supporting a crony capitalist during the general campaign.