Trump needs a ground game to win a caucus state like Iowa, no matter who endorses him, but on that point he is severely outmatched.
“…for all intents and purposes, caucuses simply require you to sit for a longer period of time and then vote. That means coming out, often in nasty weather, for caucus voters, and volunteering to count ballots and spend hours doing so for organizers. This means that the most motivated voters win.
And nobody is more motivated than the Ted Cruz crowd. Trump’s support comes from heretofore alienated subgroups, many of whom haven’t voted before. They have no history of high voter turnout. Cruz’s support comes from the traditional base in Iowa: Evangelicals and conservatives. Cruz has support from Evangelical pastors in every single Iowa precinct. He’s done the ground work. Trump hasn’t.”