A volunteer at U.S. Democratic presidential candidate Bernie Sanders's campaign event wears a shirt decorated with Sanders's image in Fort Dodge, Iowa, on January 19, 2016. #

Republican presidential candidate and former Florida Governor Jeb Bush hugs an audience member during a campaign event at Greasewood Flats Ranch, on January 29, 2016, in Carroll, Iowa. #

Congresswoman Susan Brooks speaks at a rally for U.S. Republican presidential candidate and New Jersey Governor Chris Christie at Wellman’s Pub and Rooftop in West Des Moines, Iowa, on January 31, 2016. #

Republican presidential candidate Mike Huckabee walks through a field of corn while participating in the Colonel Bud Day Pheasant Hunt hosted by Congressman Steve King outside of Akron, Iowa, on November 1, 2015. #

A Secret Service agent provides security for Republican presidential candidate Ben Carson before the start of a campaign event in Creston, Iowa, on January 22, 2016. #

Former Maryland Governor and Democratic presidential candidate Martin O'Malley plays a guitar and sings after speaking at a campaign event at Grinell College in Grinell, Iowa, on January 27, 2016. #

Republican presidential candidate and Kentucky Senator Rand Paul points to a Corvette driven by a supporter before holding a town hall at the National Sprint Car Hall of Fame and Museum in Knoxville, Iowa, on January 29, 2016. #

Magnolia Mandelko, 5, excitedly holds a campaign card and a drawing as she waits for Democratic presidential candidate Hillary Clinton, accompanied by her daughter Chelsea Clinton, to arrive at a rally at Abraham Lincoln High School in Council Bluffs, Iowa, on January 31, 2016. #

Virginia Padovan, 96, flags down Republican presidential candidate Ted Cruz for an autograph after a campaign event at Lucile's on January 26, 2016, in Centerville, Iowa. #

Former President Bill Clinton and his daughter Chelsea Clinton listen as Democratic presidential candidate Hillary Clinton speaks at a rally at Washington High School in Cedar Rapids, Iowa, on January 30, 2016. #

Workers take down a U.S. flag following a campaign stop by U.S. Democratic presidential candidate Hillary Clinton at the Family Fun Center in Adel, Iowa, on January 27, 2016. #

Shell casings lie on the floor after Republican presidential candidate Rick Santorum took target practice at the Central Iowa Impact shooting range in Boone, Iowa, on January 30, 2016. #

Republican presidential candidate Donald Trump speaks in front of his airplane during a campaign event at Dubuque Regional Airport, on January 30, 2016, in Dubuque, Iowa. #

Two women watch as Republican presidential candidate Jeb Bush departs the Cedar Falls Eagles Club in his vehicle after a campaign event on January 30, 2016, in Cedar Falls, Iowa. #

Republican presidential candidate, Senator Ted Cruz holds a news conference before a campaign event at Western Iowa Tech Community College in Sioux City, Iowa, on January 30, 2016. #

A woman photographs Republican presidential candidate Carly Fiorina as she addresses supporters and voters during a town hall style meeting at The Main Street Cafe and Bakery on January 28, 2016, in Ankeny, Iowa. #

Republican presidential candidate Senator Rand Paul fires an AR-15 rifle at an “IRS Tax Code” sign at Crossroads Shooting Sports in Johnston, Iowa, on January 17, 2016. #

Democratic presidential candidate Hillary Clinton greets a supporter during a rally at Abraham Lincoln High School, on January 31, 2016, in Des Moines, Iowa. #

A woman tries to cover the face of a protester during a campaign event for Republican presidential candidate Donald Trump at Drake University, on January 28, 2016, in Des Moines, Iowa. #

Laurie McBride watches as the campaign bus for U.S. Republican presidential candidate Ted Cruz arrives at Rustix Restaurant and Event Center in Humboldt, Iowa, on January 7, 2016. #

Democratic presidential candidate, former Maryland Governor Martin O'Malley gestures as he speaks during a town hall at Grinnell College in Grinnell, Iowa, on January 27, 2016. #

A poster supporting Republican presidential candidate Ted Cruz sits next to a Nativity scene outside the home of a supporter on January 29, 2016, in Carrol County, Iowa. #

Jim Stuart of Elgin, Iowa, listens as Democratic U.S. presidential candidate, Senator Bernie Sanders speaks during a campaign event at Wartburg College in Waverly, Iowa, on January 8, 2016. #

Republican presidential candidate, Senator Marco Rubio plays corn hole after handing out pizza to Iowa State University Students camping out for basketball tickets on campus, after speaking at a town hall at the Iowa State University Alumni Center in Ames, Iowa, on January 23, 2016. #

Supporters of Republican presidential candidate Donald Trump clamor for autographs after a campaign rally at the Gerald W. Kirn Middle School on January 31, 2016, in Council Bluffs, Iowa. #

Republican presidential candidate Senator Ted Cruz kisses his daughter Catherine, 4, as she plays on his lap while he waits offstage before being announced by radio and television personality Glenn Beck at a rally at the Five Sullivan Brothers Convention Center in Waterloo, Iowa, on January 23, 2016. #

A campaign bus carrying Democratic presidential candidate, Senator Bernie Sanders travels down the road after a campaign event at Luther College on January 24, 2016, in Decorah, Iowa. #