Trump’s Iowa loss definitely had an effect on the perception people have of him, at least somewhat.
He likes to brag that winning is his thing, the polls had him winning (yes, they are sometimes wrong), but ‘on paper’ it cleary looked as though he should win, perhaps even significantly.
He also overestimated his own ground game while underestimating Cruz’s.
Cruz had Trump on defense in the final weeks, particularly the last one, as well Cruz convinced many late deciders that he was the better choice.
He's a sleazy and slimy as they come, a novice, has no common sense, and would lose to any Dem who is the nominee.