In February 2018, Harris announced that she would be challenging three-term incumbent US Senator Tom Carper in the Democratic primary election.[4] She ran on a platform supporting Medicare for All, universal pre-K, a $15 an hour minimum wage, and criminal justice reform, among other progressive proposals.[5][1][6] Harris identifies as a progressive, but has said she "doesn't necessarily consider herself" a democratic socialist.[7] She received endorsements from progressive groups and individuals, including Justice Democrats, Our Revolution, state representative Sean Lynn, and future congresswomen Alexandria Ocasio-Cortez, Ilhan Omar, and Ayanna Pressley.[8][9][10][11][12][13] Ocasio-Cortez held multiple rallies with Harris in Delaware after Harris assisted her with her own successful primary campaign against incumbent congressman Joe Crowley.[14][15] Harris lost to incumbent Senator Tom Carper in the September 2018 primary, receiving 35% of the vote. Despite her loss, Harris received the highest vote share of a Democratic primary candidate challenging a statewide incumbent in Delaware in 20 years.[16][17][18]
Harris announced in January 2022 that she would be launching a campaign for the Delaware House of Representatives in the 32nd district. Harris defeated three other candidates in the Democratic primary, receiving 65% of the vote.[19][3] She defeated Republican Cheryl Precourt in the general election on November 8, 2022, by a 16-point margin.[20][21]
Following Carper's retirement announcement in 2023, it was reported that Harris was looking at a 2024 run for U.S. House, since the seat will be vacant due to incumbent Representative Lisa Blunt Rochester's campaign for Carper's U.S. Senate seat.[22][23] Harris ultimately decided against running.
In June 2023, Harris was elected majority whip for the Democrats in the Delaware House of Representatives.[24]