See Pictures From a Week of Campaigning in Iowa

Ted Cruz greets supporters at his rally in Des Moines, Iowa on Jan. 31, 2016.

Hillary Clinton campaigns with Bill Clinton in Davenport, Iowa, on Jan. 29, 2016.

Bernie Sanders speaks during a campaign rally and concert in Iowa City, Iowa on Jan. 30, 2016.

New Jersey Gov. Chris Christie speaks to supporters at a campaign town hall in Pella, Iowa, on Jan. 29.

Ben Carson speaks to supporters in Iowa City, Iowa, on Jan. 29.

Former Arkansas Gov. Mike Huckabee and his wife, Janet, campaign at the Crossroads shooting range in Johnston, Iowa on Jan. 30, 2016.

Martin O'Malley walks during a canvas launch at a supporter's home in Johnston, Iowa on Jan. 31.

Hillary Clinton speaks during a campaign rally in Davenport, Iowa, on Jan. 29, 2016.

Republican presidential candidate Marco Rubio appeared at a caucus event with his family on Feb. 1, 2016, at the 7 Flags Event Center in Clive, Iowa.

Donald Trump greets supporters at a rally in Des Moines, Iowa, on Jan. 26, 2016.