FILE - In this Oct. 23, 2015, file photo, Democratic presidential candidate, Sen. Bernie Sanders, I-Vt., speaks during a concert hosted by his campaign in Davenport, Iowa. For Sanders, victory in Iowa’s kickoff presidential caucuses hinges on a simple proposition: that his message of political revolution will inspire people who typically stay home on that deep-winter night. (AP Photo/Charlie Neibergall, File)