Theresa Greenfield defeated Michael Franken, Kimberly Graham, and Eddie Mauro to win the Democratic primary for U.S. Senate in Iowa. As of 9:30 p.m. Central Time, Greenfield had received 44.9% of the vote with 6% of precincts reporting. Franken followed with 26.6%, while Graham had 15.6%, and Mauro had 11.7%. A fifth candidate, Cal Woods, withdrew on May 4 and endorsed Franken. Greenfield will face first-term Sen. Joni Ernst (R) in the general election.

Greenfield will face incumbent Joni Ernst (R) in the general election. Ernst was first elected in 2014, winning 52% of the vote.