This concisely explains why this poll, which has otherwise correctly predicted every race since 1988, is most likely flawed this time around: (at least) two of its fundamental assumptions are not true this election. Specifically:
(a) Trump is not a mainstream GOP candidate, and
(b) Trump is not running a competent campaign
garbage in/garbage out - if the premises are false, then the conclusion is false, or at least, its truth-value cannot be determined on the basis of the remainder of the argument.