FiveThirtyEight has something they call ‘polling-plus‘, which takes into account more variables than simple polling. In their latest polling-plus forecast for the Republican caucuses in Iowa, they predict Ted Cruz has the best chance of winning Iowa and by a good margin:
Now if you switch to their ‘polls-only’ forecast, then the race is basically neck and neck:
Now you Trump fans can dismiss this as crap but realize when you do, they have Trump winning in their other polling-plus early state forecasts by significant margins:
New Hampshire: Trump 57% chance of winning and Cruz only 8%.
South Carolina: Trump 63% and Cruz only 18%.
Nevada: Trump 31% and Cruz 19%.