[12] In this election, the Democratic Party made a net gain of three Senate seats and the vice presidency, giving them a majority for the first time since 2014, albeit by a narrow 50–50 margin.

[a][13] Democrats unseated four Republicans in Arizona, Colorado, and both elections in Georgia – while Republicans flipped a seat in Alabama; however, Democrats under-performed expectations overall; despite record-breaking turnout and fund-raising efforts, they failed to flip several seats that were considered competitive, and lost many races by much larger margins than expected.

[17][18] Vice President Kamala Harris's tie-breaking vote gave Democrats control of the chamber by the smallest margin possible after the new administration took office.

Alabama is one of the country's most Republican states, and Jones's win was in part due to sexual assault allegations against nominee Roy Moore during the special election; most analysts expected the seat to flip back to GOP control.

[102] After Kyl resigned at the end of the year, Ducey appointed outgoing U.S. Representative Martha McSally to replace him after she lost the election to the other Arizona senate seat.

[103] McSally ran in the 2020 special election to fill the remaining two years of the term,[104] losing to Democrat Mark Kelly, a former astronaut.

Incumbent Republican Martha McSally was appointed to McCain's seat two months after losing the 2018 Arizona U.S. Senate election to Democrat Kyrsten Sinema.

McSally also suffered from low approval ratings due to her strong allegiance to Trump, who was unpopular in Arizona despite having won the state by 3.5 points in 2016.

[115] Hickenlooper is a popular former governor of Colorado, and led Gardner by as much as 20 percentage points in polls, with most pundits considering him a heavy favorite.

Gardner was Colorado's only Republican statewide officeholder, and the once purple state has trended increasingly Democratic since his narrow win in 2014.

Gardner also had low approval ratings due to his strong allegiance to Trump, who lost Colorado in 2016 to Hillary Clinton by 4.9%, and in 2020 to Joe Biden by 13.5%.

[127] Jon Ossoff, a former congressional candidate, documentary film producer, and investigative journalist, defeated former Columbus mayor Teresa Tomlinson and 2018 lieutenant governor nominee Sarah Riggs Amico in the Democratic primary to secure nomination.

[147] Antiwar activist Marilyn Jordan Lawlor[148] and state representative Anne Stava-Murray[149] briefly challenged Durbin in the Democratic primary, but both ended up withdrawing.

[154] Greenfield won the Democratic nomination, defeating former vice-admiral Michael T. Franken, attorney Kimberly Graham, and businessman Eddie Mauro in the primary.

[160][161] Barbara Bollier, a state senator and former Republican,[162] defeated former congressional candidate Robert Tillman[163] for the Democratic nomination, but lost to Marshall with a more than expected 11.4 point margin.

[178][179] On August 24, 2020, perennial candidate Vermin Supreme launched a write-in campaign for the Libertarian nomination,[180] but received too few votes to qualify for the general election ballot.

[192] This race was an exact rematch of the 2018 Mississippi Senate special election, in which Hyde-Smith defeated Espy for the remaining two years of the seat's term.

[196] Daines was opposed (before his nomination) in the Republican primary by hardware store manager Daniel Larson and former Democratic speaker of the Montana House of Representatives John Driscoll, who changed parties in 2020.

After the primary election, the Nebraska Democratic party withdrew its support from Janicek when allegations that he sexually harassed a campaign staffer emerged.

[203] Janicek refused to leave the race despite the state party endorsing his former primary opponent,[clarification needed] which led former Democratic Congressman Brad Ashford to announce a write-in campaign on August 23, 2020.

[204][205] After Janicek vowed to remain in the race anyway, Ashford withdrew on August 27, citing lack of time and resources necessary for a U.S. Senate campaign.

[206] The state Democratic Party subsequently threw its support behind long-time Nebraska activist Preston Love Jr., who declared a write-in candidacy for the seat.

Interior Department official Gavin Clarkson and executive director for the New Mexico Alliance for Life Elisa Martinez in the primary.

Cunningham defeated state senator Erica D. Smith and Mecklenburg County commissioner Trevor Fuller for the Democratic nomination.

Despite having grown unpopular among both centrist and conservative Republicans due to his inconsistent support of Trump, and trailing narrowly in polls for almost the entire cycle,[231] Tillis won re-election by nearly 2 points.

Inhofe defeated J.J. Stitt, a farmer and gun shop owner, and Neil Mavis, a former Libertarian Party candidate, for the Republican nomination.

Environmental activist Marquita Bradshaw of Memphis defeated James Mackler, an Iraq War veteran and Nashville attorney,[263] in the Democratic primary, a major upset.

Statewide races in Texas have been growing more competitive in recent years, and polling in August/September showed Cornyn with a lead of 4–10 points over Hegar, with a significant fraction of the electorate still undecided.

Capito was unsuccessfully challenged in the Republican primary by farmer Larry Butcher and Allen Whitt, president of the West Virginia Family Policy Council.

[284] Ben-David, the chair of the Department of Zoology and Physiology at the University of Wyoming, defeated community activists Yana Ludwig and James Debrine, think-tank executive Nathan Wendt, and perennial candidates Rex Wilde and Kenneth R. Casner for the Democratic nomination.