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Heart vs. head in Iowa’s Democratic faceoff

The idiosyncratic and critically important Iowa caucuses will test whether Sanders' enthusiasm beats Clinton's pragmatism.

Democratic presidential candidates Martin O'Malley, Hillary Clinton and Bernie Sanders (gather after the NBC, YouTube Democratic presidential debate at the Gaillard Center, January 17, 2016, in Charleston, S.C.Photo by Mark Peterson/Redux for MSNBC

Alex Seitz-Wald