In three man race nobody is going to have a 28 pt lead going forward but you only need 2-3 pts to win. A 2 pt win is a win.
True, but it is also about perception. If Trump goes from a 28 point lead to a 2 point win in a week, the perception is going to be that he is falling fast. That would be two elections in a row where he performed much worse than the polls indicated, which would make everyone start to question all of the other polls showing him in the lead.
And since like Iowa, NH is a proportional state, that 2-pt lead will mean an extra 1 delegate over the number two finisher.