Rick Santorum, former senator from Pennsylvania and 2016 Republican presidential candidate, speaks during a Donald Trump, president and chief executive of Trump Organization Inc. and 2016 Republican presidential candidate, not pictured, campaign event at Drake University in Des Moines, Iowa, U.S., on Thursday, Jan. 28, 2016. Trump, according to a flurry of early-state and national polls, is the overwhelming favorite of self-identified moderate and liberal Republican voters. Among more conservative voters, he often trails his chief rival for the nomination, U.S. Senator Ted Cruz. Photographer: Patrick T. Fallon/Bloomberg via Getty Images