probably because Trump can bring in disaffected Democrats and independents who are tired of Uppity Hussein’s love Islam and transvestites, and “campus rape” crap but who aren’t into the GOPe’s dogma on trade and SS/medicare
Trump can bring in ignorant leftists, populists, and low-skilled and uneducated voters by pandering to them, not by running as a conservative. Suggesting that Trump is a uniter or has a Reagan-like wide appeal is patently false; Trump brings in additional support at the expensive of Constitutional conservatives and moderate Republicans alike.