In a word: "Iowa."
In two words: "Religious Right."
In two more words: "Local organization."
The two phrases are both important in Iowa, the first just on the GOP side, the second on both parties' plates.
Rick Santorum and Mike Huckabee illustrate the former, from previous campaigns, especially Santorum.
Jimmy Carter is the exemplar of the second. Without the Iowa caucuses, and his local-level groundwork, he doesn't win in 1976, possibly.
The Donald's campaign, from what's publicly apparent, at least, strikes me as a very top-down big business type structure. Not geared for Iowa, but we'll see.
It seems to me that local caucus meetings will get either him, or ground-level representatives into making politically contradictory statements down the line.
And, despite some of his current appeal to tea party types, he's NOT a Religious Right type. In fact, his description of taking communion makes him sound like he's intermittently religiously observant.
If he can stay in the top three in Iowa, he might do well in New Hampshire, which allows crossover voting. But, he'll then struggle in Nevada and bomb in South Carolina.
As to who benefits, assuming I'm correct? I have no idea; Trump's constituency doesn't fit more professionalized definitions of who today's GOP is. Tea partiers who like him obviously haven't read his stance on social issues, if that's of importance to them.
Trump is saying he's in to win, and disavows notions that he'll cut and run if he starts sinking. Yeah, sure. Steve Forbes likely said something similar 20-plus years ago.