It is and I am sure Trump knows this (though not his fanatical supporters). Cruz just ran a better operation in Iowa and Trump all but admitted as much. Trump would rather as many people as possible dwell on his fraud accusations rather than see plainly that Ted out-campaigned him and that "the Donald" is no longer inevitable (he never was, but again Trump has to keep his supporters wearing blinders).
Trump is way ahead in the polls right now in NH, but if his lead dwindles and he somehow loses there too I am not sure if he will even stay in the race past South Carolina (assuming he loses that one too).
If he manages to blow that lead in NH, he is gone.