The 2010 United States Senate elections were held on November 2, 2010, from among the United States Senate's 100 seats. A special election was held on January 19, 2010, for a mid-term vacancy in Massachusetts. Thirty-four of the November elections were for six-year terms to the Senate's Class 3, while other three were special elections to finish incomplete terms. Those 37 November elections featured 19 incumbent Democrats (seven of whom retired or were defeated in the primary) and 18 incumbent Republicans (eight of whom retired or were defeated in the primary).

Quick Facts 37 of the 100 seats in the United States Senate 51 seats needed for a majority, Majority party ...

2010 United States Senate elections

← 2008 November 2, 2010[lower-alpha 1] 2012 →
37 of the 100 seats in the United States Senate 51 seats needed for a majority
Majority party Minority party   Leader Harry Reid Mitch McConnell Party Democratic Republican Leader's seat Nevada Kentucky Seats before 57 41 Seats after 51 47 Seat change 6 6 Popular vote 32,405,787[1] 34,616,463 Percentage 45.1% 48.2% Seats up 19 18 Races won 13 24   Third party   Party Independent Seats before 2[lower-alpha 2] Seats after 2[lower-alpha 3] Seat change Popular vote 155,846 Percentage 0.2% Seats up 0 Races won 0
Results of the elections: (excl. Massachusetts)      Democratic hold      Republican hold      Republican gain      No election Rectangular inset (N.Y.): both seats up for election
Majority Leader before election Harry Reid Democratic Elected Majority Leader Harry Reid Democratic

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After the 2008 elections, the Senate was composed of 58 Democrats, 40 Republicans, and 2 independents who caucused with the Democrats. However, in a January 2010 special election, Republicans picked up a seat in Massachusetts thereby reducing Democrats' majority to 57 seats.

Republicans won four seats held by retiring Democrats and also defeated two incumbent Democrats, for a Republican net gain of six seats. This was the first time since 1994 that Republicans successfully defended all of their own seats. This was also the fourth consecutive election of Class 3 senators where Democrats failed to gain seats. Despite the Republican gains, the Democrats retained a majority of the Senate with 51 seats plus the two independents who caucused with them, compared to the 47 Republican seats. As of 2023^[update], this was the last time Republicans won U.S. Senate seats in Illinois and New Hampshire.

Shading indicates party with largest share of that line. Does not include the January 2010 special election in Massachusetts.

More information Parties, Total ...

Parties									Total
		Democratic	Republican	Independent	Libertarian	Green	Constitution	Others
Last elections (2008) Before the November elections		57	41	2[lower-alpha 3]	—	—	—	—	100
Not Up	Total	38	23	2[lower-alpha 3]	—	—	—	—	63
	Class 1 (2006→2012)	19	10	2[lower-alpha 3]	—	—	—	—	31
	Class 2 (2008→2014)	19	13	—	—	—	—	—	32
Up	Total	19	18	—	—	—	—	—	37
	Class 1	2	—	—	—	—	—	—	2
	Class 2	1	—	—	—	—	—	—	1
	Class 3	16	18	—	—	—	—	—	34
Incumbent retired	Total before	6[lower-alpha 4]	6	—	—	—	—	—	12
	Held by same party	3	6	—	—	—	—	—	9
	Replaced by other party	3 Democrats replaced by 3 Republicans		—	—	—	—	—	3
	Result after	3	9	—	—	—	—	—	12
Incumbent ran	Total before	13[lower-alpha 5][lower-alpha 6]	12[lower-alpha 7]	—	—	—	—	—	25
	Won election	10[lower-alpha 5]	10	—	—	—	—	—	20
	Lost re-election	2 Democrats replaced by 2 Republicans		—	—	—	—	—	2
	Lost renomination but won re-election	—	1	—	—	—	—	—	1
	Lost renomination but party held	—	1	—	—	—	—	—	1
	Lost renomination and party lost	1 Democrat replaced by 1 Republican		—	—	—	—	—	1
	Result after	10[lower-alpha 5]	15	—	—	—	—	—	25
Total elected		13[lower-alpha 5]	24	—	—	—	—	—	37
Net gain/loss		6	6	—	—	—	—	—	6
Nationwide vote	Votes	32,405,787	34,616,463	155,846[lower-alpha 8]	776,327	552,006	178,860	3,100,833[lower-alpha 8]	71,786,122
	Share	45.14%	48.22%	0.22%	1.08%	0.77%	0.25%	4.32%	100%
Result		51	47	2[lower-alpha 3]	—	—	—	—	100
End of this Congress		56	42	2[lower-alpha 3]	—	—	—	—	100

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Source: Clerk of the U.S. House of Representatives^[1]

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 reelection) 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

Where a site gives a percentage probability as its primary indicator of expected outcome, the chart below classifies a race as follows:

• Tossup: 50-55%
• Tilt: 56-60%
• Lean: 61-75%
• Likely: 76-93%
• Safe: 94-100%

Seven November races, as well as the Massachusetts special election in January, had margins less than 10%:

California was the tipping point state, where Barbara Boxer (D) defeated Carly Fiorina (R) by a margin of 10.0%.

Quick Facts Nominee, Party ...

Alabama election

← 2004 2016 →

Nominee Richard Shelby William G. Barnes Party Republican Democratic Popular vote 967,861 515,049 Percentage 65.3% 34.7%

County results Shelby:      50–60%      60–70%      70–80%      80–90% Barnes:      50–60%      60–70%      70–80%      80–90%

U.S. senator before election Richard Shelby Republican Elected U.S. Senator Richard Shelby Republican

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Incumbent Republican Richard Shelby won re-election to a fifth term. On November 9, 1994, Shelby switched his party affiliation from Democratic to Republican, one day after the Republicans won control of both houses in the midterm elections, giving the Republicans a 53–47 majority in the Senate. He won his first full term as a Republican in 1998 by a large margin, and faced no significant opposition in 2004 and 2010.

Shelby had over $17 million in the bank, one of the highest of any candidate in the country. He had become even more popular in his opposition to the Troubled Asset Relief Program (TARP) and the Emergency Economic Stabilization Act of 2008, as the ranking member of the Senate Banking Committee.

In May, Shelby told reporters "I don't even know who my opponent is."^[8]

Quick Facts Candidate, Party ...

Alaska election

← 2004 2016 →

Candidate Lisa Murkowski Joe Miller Scott McAdams Party Republican Republican Democratic Popular vote 101,091 90,839 60,045 Percentage 39.5% 35.5% 23.5%

Borough and census area results Murkowski:      40–50%      50–60%      60–70%      70–80% Miller:      30–40%      40–50%      50–60% McAdams:      30–40%      40–50%

U.S. senator before election Lisa Murkowski Republican Elected U.S. Senator Lisa Murkowski Republican

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The November general election in Alaska was preceded by primary elections which were held August 24, 2010. Scott McAdams, the Mayor of Sitka, became the Democratic nominee and Joe Miller, an attorney and former federal magistrate, became the Republican nominee after defeating incumbent Senator Lisa Murkowski^[10] in the Republican primary.^[11]

Murkowski garnered more than 100,000 write-in votes in the general election, many^{[clarification needed]} of which were challenged by Miller for various errors including minor misspellings. The appeal was denied^[12] Even if all the challenged votes were thrown out, Murkowski would have still had a lead of over 2,100 votes.^[13]

Quick Facts Nominee, Party ...

Arizona election

← 2004 2016 →

Nominee John McCain Rodney Glassman Party Republican Democratic Popular vote 1,005,615 592,011 Percentage 58.7% 34.5%

McCain:      40–50%      50–60%      60–70% Glassman:      50–60%

U.S. senator before election John McCain Republican Elected U.S. Senator John McCain Republican

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Incumbent Republican John McCain, who returned to the Senate after losing the presidency to Barack Obama in the 2008 presidential election, ran for re-election to a fifth term and won.^[19]

After spending over $20 million during the primaries, McCain still had more than $1million cash on hand after the primary election. Glassman criticized McCain on women's issues.^[21] In August 2010, Glassman released a TV advertisement called "Arizona First."^[22]

Quick Facts Nominee, Party ...

Arkansas election

← 2004 2016 →

Nominee John Boozman Blanche Lincoln Party Republican Democratic Popular vote 451,617 288,156 Percentage 57.90% 36.95%

Boozman:      40–50%      50–60%      60–70%      70–80% Lincoln:      40–50%      50–60%      60–70%

U.S. senator before election Blanche Lincoln Democratic Elected U.S. Senator John Boozman Republican

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Incumbent Democrat Blanche Lincoln ran for re-election to a third term, but lost to Republican nominee John Boozman. Boozman became the first Republican in 138 years to win the seat. Arkansas had previously only elected one Republican senator since the Reconstruction, who was defeated after his first term in 2002 by Mark Pryor.

The Republican primary was held May 18, 2010, with early voting from May 3–17.

Quick Facts Nominee, Party ...

California election

← 2004 2016 →

Nominee Barbara Boxer Carly Fiorina Party Democratic Republican Popular vote 5,218,441 4,217,366 Percentage 52.2% 42.2%

County results Boxer:      40–50%      50–60%      60–70%      70–80%      80–90% Fiorina:      40–50%      50–60%      60–70%      70–80%

U.S. senator before election Barbara Boxer Democratic Elected U.S. Senator Barbara Boxer Democratic

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Incumbent Democrat Barbara Boxer won re-election to a fourth term.

In 2009, Boxer was criticized for correcting a general who called her "ma'am". Brigadier General Michael Walsh was testifying on the Louisiana coastal restoration process in the wake of Hurricane Katrina and answered Boxer's query with "ma'am" when Boxer interrupted him. "Do me a favor," Boxer said. "can you say 'senator' instead of 'ma'am?'" "Yes, ma'am," Walsh interjected. "It's just a thing, I worked so hard to get that title, so I'd appreciate it. Thank you," she said. The Army's guide to protocol instructs service members to call members of the U.S. Senate "sir", "ma'am" or "senator".^[28][29] Fiorina used this incident prominently in campaign ads, as did David Zucker, who directed a humorous commercial for RightChange.com titled 'Call Me Senator.' In February 2010, Carly Fiorina put out a campaign ad attacking Republican rival Tom Campbell featuring a "demon sheep", creating international, mostly negative, publicity.^[30]

Quick Facts Nominee, Party ...

Colorado election

← 2004 2016 →

Nominee Michael Bennet Ken Buck Party Democratic Republican Popular vote 851,590 822,731 Percentage 48.1% 46.4%

County results Bennet:      40–50%      50–60%      60–70%      70–80% Buck:      40–50%      50–60%      60–70%      70–80%

U.S. senator before election Michael Bennet Democratic Elected U.S. Senator Michael Bennet Democratic

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In December 2008, President-elect Barack Obama selected incumbent U.S. Senator Ken Salazar to become U.S. Secretary of the Interior.^[31] After Salazar resigned from his seat,^[32] Democratic Governor Bill Ritter appointed Denver Public Schools Superintendent Michael Bennet to fill the seat, who won re-election to his first full term.^[33][34]

This was one of the most expensive elections in the 2010 cycle, with more than $50 million spent total, including over $35 million in outside spending.^[36] Conservative third party groups hammered Bennet for voting 92% of the time with the Democratic leadership, including voting for healthcare reform and the stimulus package.^[37] Liberal third party groups called Buck extremist. Bennet focused on attacking Buck's views on abortion, which he believed should be banned including those of cases of rape and incest. He was also attacked for wanting to eliminate the 17th Amendment^[38] and refusing to prosecute an alleged rapist as Weld County district attorney. Planned Parenthood mounted a mail campaign, targeting women voters with the warning that "Colorado women can't trust Ken Buck." Bennet won the women vote by 17 points according to exit polls. After the election, Buck conceded to the Denver Post that the main reason why he lost is because of social issues.^[39]

Quick Facts Turnout, Nominee ...

Connecticut election

← 2004 2016 →
Turnout	45.9% (voting eligible)
Nominee Richard Blumenthal Linda McMahon Party Democratic Republican Popular vote 636,040 498,341 Percentage 55.2% 43.2%
County results Municipality results Blumenthal:      40–50%      50–60%      60–70%      70–80%      80–90% McMahon:      40–50%      50–60%      60–70%
U.S. senator before election Chris Dodd Democratic Elected U.S. Senator Richard Blumenthal Democratic

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Incumbent Democrat Christopher Dodd suffered from dropping approval ratings in the past few years due to major controversies, leading him to announce in January 2010 that he would retire, instead of seeking a sixth term.^[42] As Dodd was a Democrat, Richard Blumenthal, incumbent State Attorney General, announced on the same day that he would run for Dodd's seat.^[43] The Connecticut Democratic Party nominated Blumenthal on May 21. Businesswoman Linda McMahon won the state party's nominating convention and the August 10 Republican primary to become the Republican candidate.^[44]

Note: Blumenthal also appeared on the line of the Connecticut Working Families Party and received 30,836 votes on it. His Working Families and Democratic votes have been aggregated together on this table.

Quick Facts Nominee, Party ...

Delaware special election

← 2008 2014 →

Nominee Chris Coons Christine O'Donnell Party Democratic Republican Popular vote 174,012 123,053 Percentage 56.6% 40.0%

County results Coons:      60–70% O'Donnell:      50–60%

U.S. senator before election Ted Kaufman Democratic Elected U.S. Senator Chris Coons Democratic

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This was a special election to fill Delaware's Class 2 Senate seat, then held by Ted Kaufman, an appointee. The seat had been previously held by long-time Senator Joe Biden, who vacated it when he became Vice President of the United States in 2009.

Quick Facts Nominee, Party ...

Florida election

← 2004 2016 →

Nominee Marco Rubio Charlie Crist Kendrick Meek Party Republican Independent Democratic Popular vote 2,645,743 1,607,549 1,092,936 Percentage 48.9% 29.7% 20.2%

Rubio:      30–40%      40–50%      50–60%      60–70%      70–80% Crist:      30–40%      40–50% Meek:      40–50%      50–60%      60–70%

U.S. senator before election George LeMieux Republican Elected U.S. Senator Marco Rubio Republican

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Incumbent Republican Senator Mel Martínez, who was elected in a very close race against Democrat Betty Castor with 49% of the vote in 2004, announced on December 2, 2008, that he would not run for re-election to a second term,^[49] then announcing on August 7, 2009, that he would resign prior to the end of his term.^[50] The Governor of Florida, Republican Charlie Crist, was required to appoint a successor and he chose his former Chief of Staff, George LeMieux. LeMieux, a placeholder who did not run in the election, replaced Martínez in the Senate on September 10, 2009.

Crist publicly announced he was running for the seat in mid-2009. When he declared his candidacy, he received many Republican endorsements, including the National Republican Senatorial Committee, Martínez, and 2008 Republican presidential nominee John McCain. However, his support of the American Recovery and Reinvestment Act of 2009 hurt his popularity among conservatives, and Tea Party candidate Marco Rubio, the former Speaker of the Florida House of Representatives, surged in the polls. In April 2010, Crist announced he would drop out of the Republican primary and run as an Independent. The National Republican Senatorial Committee withdrew its endorsement of Crist and demanded a refund of its campaign funds that it provided for the Crist campaign.^[51][52][53] Rubio went on to win the Republican primary against only token opposition.

Polling initially showed Crist neck and neck with Rubio, but by the end of August Rubio opened up a solid and consistent lead. He was supported by Republican and some Independent voters whereas Democratic and other Independents were split between Crist and Meek. Rubio went on to win the election with 49% of the vote to Crist's 30% and Meek's 20%.