2018 United States Senate elections

Among the 33 Class 1 Senate seats up for regular election in 2018, twenty-three were held by Democrats, two by independents who caucused with the Senate Democrats and eight by Republicans. Class Two seats in Minnesota and Mississippi held by interim appointees were also up for election; both incumbent appointees sought election to finish their unexpired terms. Democrats targeted Republican-held Senate seats in Arizona (open seat) and Nevada. Mississippi (at least one of the two seats) and Tennessee (open seat) were also competitive for the Democrats. Republicans targeted Democratic-held seats in Indiana, Missouri, Montana, North Dakota and West Virginia, all of which were won by Republicans in both the 2012 and 2016 presidential elections. Seats in Florida, Ohio, Pennsylvania, Wisconsin and Michigan, all of which were won by Obama in 2008 and 2012 but by Trump in 2016, were also targeted by Republicans. The Democratic-held seat in New Jersey was also considered unexpectedly competitive due to corruption allegations surrounding the Democratic incumbent. The map was widely characterized as extremely unfavorable to Democrats, as Democrats were defending 26 states while Republicans were defending nine. Of these seats, Democrats were defending ten in states won by Donald Trump in the 2016 presidential election, while Republicans were only defending one seat in a state won by Hillary Clinton in 2016. According to FiveThirtyEight, Democrats faced the most unfavorable Senate map in 2018 that any party has ever faced in any election. == Results summary ==

Source: Clerk of the U.S. House of Representatives. == Change in composition ==

Each block represents one of the one hundred seats in the Senate. "D#" is a Democratic senator, "I#" is an independent senator and "R#" is a Republican senator. Arranged so parties are separated and a majority is clear by crossing the middle. Before the elections Each block indicates an incumbent senator's actions going into the election. Some "Ran" for re-election, some "Retired," and those without a note were not up for election this cycle. Before the elections, Republicans held 51 seats, Democrats held 47, and Independents held 2. After the 2017 Senate special election in Alabama on the start of the second session in the 115th Congress. After the elections Some senators were "Re-elected," some were a "Gain" in the seat from the other party (either by beating an incumbent or by winning an open seat), some were a "Hold" by the same party but with a different senator, and those without a note were not up for election this year. After these elections, Democrats had 45 seats, independents had 2, and Republicans had 53. == Predictions ==

Several sites and individuals publish predictions of competitive seats. These predictions look at factors such as the strength of the incumbent (if the incumbent is running for re-election) and the other candidates, and the state's partisan lean (reflected in part by the state's Cook Partisan Voting Index rating). The predictions assign ratings to each seat, indicating the predicted advantage that a party has in winning that seat. Most election predictors used: • "tossup": no advantage • "tilt" (used by some predictors): advantage that is not quite as strong as "lean" • "lean": slight advantage • "likely" or "favored": significant, but surmountable, advantage • "safe" or "solid": near-certain chance of victory == Election dates ==

These are the election dates for the regularly scheduled general elections. == Gains and losses ==

Retirements Three Republicans retired instead of seeking re-election. Defeats Four Democrats and one Republican sought re-election but lost in the general election. Post-election changes One Republican resigned before the start of the 116th Congress on December 31, 2018, and another Republican resigned during the 116th Congress for health reasons. Initially, all were replaced by Republican appointees. == Race summary ==

Special elections during the preceding Congress In these special elections, the winners will be seated before January 3, 2019, when elected and qualified. They are ordered by election date, then by state and by class. Elections leading to the next Congress In these general elections, the winners were elected for the term beginning January 3, 2019. All of the elections involve the Class 1 seats and they are ordered by state. == Closest races ==

In twelve races the margin of victory was under 10%. == Arizona ==

One-term Republican Jeff Flake was elected with 49% of the vote in 2012. He chose not to run for re-election. U.S. Representative Martha McSally won the Republican nomination in a three-way primary on August 28, 2018, against Joe Arpaio and Kelli Ward. U.S. Representative Kyrsten Sinema easily secured the Democratic nomination. Sinema defeated McSally by a slim margin; her victory became official only after six days of counting ballots. == California ==

Four-term Democrat Dianne Feinstein won a special election in 1992 and was elected to full terms in 1994, 2000, 2006, and 2012. She ran for re-election and advanced to the general election after securing the top spot in the June 5 jungle primary. The June 5 primary ballot listed 32 candidates (Feinstein plus 31 challengers) in addition to 3 write-in candidates. There were 10 Democratic candidates, 11 Republican candidates, one Libertarian, one Peace and Freedom candidate, and 9 independent candidates. There was also a Green Party candidate who ran as a write-in. President pro tempore of the California State Senate Kevin de León advanced to the general election for the right to challenge Feinstein after securing the second spot in the primary. On November 6, Dianne Feinstein was elected to a fifth term, defeating Kevin de León. == Connecticut ==

| map_size = 200px | map_caption = Murphy: Corey: | title = U.S. senator | before_election = Chris Murphy | before_party = Democratic Party (US) | after_election = Chris Murphy | after_party = Democratic Party (US) }} One-term Democrat Chris Murphy was elected with 55% of the vote in 2012. He ran for re-election. Businessmen Matthew Corey received the Republican nomination. Chris Murphy was elected to a second term, winning nearly 60% of the vote. == Delaware ==

Three-term Democrat Tom Carper won re-election with 66% of the vote in 2012. He announced he was running for re-election during an interview on MSNBC on July 24, 2017. He defeated Dover community activist Kerri Evelyn Harris for the Democratic nomination. Sussex County Councilman Robert Arlett won the Republican nomination. == Florida ==

Three-term Democrat Bill Nelson was re-elected with 55% of the vote in 2012. He sought re-election to a fourth term in office. Florida Governor Rick Scott won the Republican nomination. First elected in 2010 and re-elected in 2014, Scott's term as Governor of Florida was set to end by January 2019, due to term limits. Final recount numbers were released following a machine and hand recount with Rick Scott maintaining a lead. On November 18, Nelson conceded to Scott. Two days later, election results were certified by the state, cementing Scott's win. == Hawaii ==

One-term Democrat Mazie Hirono was elected with 63% of the vote in 2012. She ran for reelection. Ron Curtis was the Republican nominee. Hirono was elected to a second term by a landslide. == Indiana ==

One-term Democrat Joe Donnelly was elected with 50.04% of the vote in 2012. He ran for reelection. He won the Democratic primary unopposed. State Representative Mike Braun and Todd Rokita == Maine ==

One-term Independent Senator Angus King was elected in a three-way race with 53% of the vote in 2012. King has caucused with the Democratic Party since taking office in 2013, but he has left open the possibility of caucusing with the Republican Party in the future. State Senator Eric Brakey ran unopposed for the Republican nomination. Public school teacher and founder of UClass Zak Ringelstein ran unopposed for the Democratic nomination. and a June 2018 referendum sustaining the change. King was easily re-elected with over 50% of the vote. == Maryland ==

Two-term Democrat Ben Cardin was re-elected with 56% of the vote in 2012. He won the Democratic primary. Tony Campbell, Evan Cronhardt, Nnabu Eze, Gerald Smith, and Blaine Taylor were seeking the Republican nomination, with Campbell winning. Arvin Vohra, vice chairman of the Libertarian National Committee, sought the Libertarian Party nomination. == Massachusetts ==

One-term Democrat Elizabeth Warren was elected with 54% of the vote in 2012. She ran for re-election. State Representative Geoff Diehl, attorney and founder of Better for America, John Kingston ran as an independent. Shiva started as in early 2017 as the first Republican in the race, but went independent in November 2017. Warren defeated Diehl, winning a second term. == Michigan ==

Three-term Democrat Debbie Stabenow was re-elected with 59% of the vote in 2012. She was renominated without Democratic opposition. On the Republican side, businessman John James won the nomination. In the final months of the election, polls showed the race was beginning to narrow. Ultimately, Stabenow was re-elected, defeating James, with a majority of the vote. == Minnesota ==

Minnesota (regular) Two-term Democrat Amy Klobuchar was re-elected with 65% of the vote in 2012. She ran for re-election. State Representative Jim Newberger Minnesota (special) Two-term Democrat Al Franken announced that he would resign in December 2017, following allegations of sexual harassment. Mark Dayton, Governor of Minnesota, appointed Lt. Gov. Tina Smith on January 2, 2018, as an interim Senator until the November 2018 election. She defeated primary challenger Richard Painter in the Democratic primary held on August 14. Incumbent Tina Smith defeated Republican Karin Housley in the general election to finish the term ending January 3, 2021. == Mississippi ==