I find this a little hard to believe but on the other hand I only know for certain among my own circle of family, friends, and colleagues, who do vote regularly and many of whom support Trump, and many of those are Republicans. It is hard to believe that the man who is many percentage points above the other candidates is losing by double digits. There is a disconnect somewhere.
Having worked the Iowa caucus system for a number of years—I would guarantee at least a third of the claimed Trump voters to be a no show, and likely as high as half.
People always seem to have other things to do, whether or not they actually do of course—rather than spend an hour and a half or two hours at the caucus listening to party business and voting on committee members before the actual vote/standup for your candidate. I stood and spoke for/behalf of a candidate for about a thousand one year to as little as 5 another year prior to voting. This is really an effort designed to determine just how strong/determined an individual is/are (and canvas him/her) to support a candidate come general election time. You are also getting a quick look at identifying possible volunteer workers for a candidate. It honestly is not a great deal of fun for 99 percent of participants. I always thought door prizes should be awarded!