Volunteers in Des Moines make calls at the campaign headquarters of then-Democratic presidential hopeful Sen. Barack Obama on Dec. 5, 2007 ahead of the Iowa caucus. Obama has called those "fired-up" campaign workers from his 2008 campaign, one of his proudest legacies.
Rick Gershon/Getty Images
Donald Trump (right) brings the two most recent Iowa winners, Mike Huckabee (left) and Rick Santorum, on stage during Trump's rally for veterans, an event he held instead of attending the GOP debate.
Christopher Furlong/Getty Images
Texas Sen. Ted Cruz speaks during the 2015 Iowa Faith & Freedom Coalition presidential forum. He's made religion a central tenet of his campaign for the Republican presidential nomination.
Bloomberg/Bloomberg via Getty Images
Democratic presidential candidate Hillary Clinton speaks at a rally in Marshalltown, Iowa. Clinton is narrowly ahead of Sanders, but within the margin of error in the final Iowa poll.
Republican presidential candidate Donald Trump and Fox News Channel host and moderator Megyn Kelly during the first Republican presidential debate — the origin of their feud.
Thanks to the current nomination calendar, U.S. presidential candidates (like Chris Christie, pictured at the 2015 Iowa State Fair) get lots of practice at flipping pork chops.
Scott Olson/Getty Images News