I think that Trump is either, A) trying to see just how far left he can go before he starts to lose support; or B) is so confident that he is going to win the primaries that he has already started his “run to the middle (left)” for the general election.
I would answer “B”....
http://www.cnn.com/2016/01/25/opinions/trump-shoot-somebody-cult-cupp/index.html