In the 2018 gubernatorial election, Hart ran for lieutenant governor of Iowa on the Democratic ticket, with running mate Fred Hubbell.

Hart's opponent, Republican physician Mariannette Miller-Meeks, was certified as the winner by six votes, one of the closest federal elections in U.S. history.

[5] Hart served on the Senate Agriculture, Economic Growth, Education, Local Government, and Veterans Affairs committees.

[3] On June 16, 2018, Fred Hubbell announced that Hart would join the Democratic ticket as the nominee for lieutenant governor in the 2018 Iowa gubernatorial election.

[16] In her petition she contended that 22 legally cast ballots were unlawfully excluded, and two, that the 24 counties' recount boards' procedures were irregular across the district.

[19][21] In response to a letter containing questions from House Administration Committee Chair Zoe Lofgren, Hart and her attorney Marc Elias wrote, "Where necessary to effectuate the will of the voters of the Second Congressional District, the Committee should therefore exercise its discretion to depart from Iowa law, and adopt counting rules that 'disenfranchise the smallest possible number of voters.

'"[22] Republicans and some Democrats sharply criticized Pelosi's decision to review the race in the House Administration Committee, calling it an attempt to steal the election.