The 2018 United States Senate elections were held on November 6, 2018. 33 of the 100 seats were contested in regular elections while two others were contested in special elections due to Senate vacancies in Minnesota and Mississippi. The winners were elected to six-year terms running from January 3, 2019, to January 3, 2025. Senate Democrats had 26 seats up for election (including the seats of two independents who caucus with them) while Senate Republicans had nine seats up for election.
To maintain their working majority of 50 Senators and Republican Vice President Mike Pence (who can cast a tie-breaking vote), Republicans could only afford a net loss of one Senate seat in the 2018 elections. The Republicans had a 52-48 majority after the 2016 elections, but they lost a seat in Alabama in December 2017 after senator Jeff Sessions resigned to become the U.S. Attorney General and Doug Jones won the resulting special election. Three Republican-held seats were open as a result of retirements in Tennessee, Utah and Arizona, while every Democratic incumbent ran for re-election. Democrats faced what was considered an extremely unfavorable map as they were defending ten seats in states won by Donald Trump in the 2016 presidential election and 26 in total while Republicans were only defending one seat in a state won by Hillary Clinton in 2016 and nine in total. Additionally, Democrats were defending five seats in states that Trump won by double digits in 2016.
The Republicans maintained and increased their majority, defeating Democratic incumbents in Florida, Indiana, Missouri and North Dakota. Democrats won two Republican-held seats, defeating incumbent Dean Heller in Nevada and winning an open seat in Arizona that was previously held by Jeff Flake.