If Trump wins, he wins, just as Cruz actually won Iowa, no matter what Trump and his people say.
However, if he gets a mere 28 percent after polling much higher than that, it will be the second straight state in which he will have underperformed. Should that occur, it should be of some concern to the Trump people.
As I have always said here I have no faith in polls ever. If I ever do take a poll which I have not done for years I toy with them. Most people I know mislead pollsters. I resent pollsters nosing into my business at dinner time with multiple choice questions without any option to answer what I really think.