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 midterm vacancy in Massachusetts. 34 of the November elections were for 6-year terms to the Senate's Class 3, while other 3 were special elections to finish incomplete terms. Those 37 November elections featured 19 incumbent Democrats (7 of whom retired or were defeated in the primary) and 18 incumbent Republicans (8 of whom retired or were defeated in the primary).

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 4 seats held by retiring Democrats and also defeated 2 incumbent Democrats, for a Republican net gain of 6 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 2 Independents who caucused with them, compared to the 47 Republican seats. , this was the last time Republicans won U.S. Senate seats in Illinois and New Hampshire.

Results summary

+ ↓ 51 2 47 Democratic Independent Republican

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

Parties Total Democratic Republican Independent Libertarian Green Constitution Others Last elections (2008)Before the November elections 57 41 2 — — — — 100 Not Up Total 38 23 2 — — — — 63 19 10 2 — — — — 31 19 13 — — — — — 32 Up Total 19 18 — — — — — 37 2 — — — — — — 2 1 — — — — — — 1 16 18 — — — — — 34 Incumbentretired Total before 6 6 — — — — — 12 3 6 — — — — — 9 3 Democrats replaced by 3 Republicans — — — — — 3 Result after 3 9 — — — — — 12 Incumbentran Total before 13 12 — — — — — 25 10 10 — — — — — 20 2 Democrats replaced by 2 Republicans — — — — — 2 — 1 — — — — — 1 — 1 — — — — — 1 1 Democrat replaced by 1 Republican — — — — — 1 Result after 10 15 — — — — — 25 Total elected 13 24 — — — — — 37 Net gain/loss 6 6 — — — — — 6 Nationwide vote Votes 32,405,787 34,616,463 155,846 776,327 552,006 178,860 3,100,833 71,786,122 Share 45.14% 48.22% 0.22% 1.08% 0.77% 0.25% 4.32% 100% Result 51 47 2 — — — — 100 End of this Congress 56 42 2 — — — — 100

Source: Clerk of the U.S. House of Representatives

Change in composition

After the January special election D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D Majority → D R I I D D D D D D R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R

Before the November elections D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D Majority → D R I I D D D D D D R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R

Result of the November elections D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D D Majority → D R R R R R R R I I R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R

Key: D Democratic I Independent R Republican

Final pre-election 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 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%

Constituency Incumbent 2010 election ratings State Senator Lastelection Cook Rothenberg RCP Sabato CQ Politics Result Alabama 67.5% R Shelby65.2% R Alaska 48.6% R Murkowski 39.5% R Arizona 76.7% R McCain59.2% R Arkansas 55.9% D Boozman57.9% R California 57.7% D Boxer 52.2% D Colorado Appointed Bennet48.1% D Connecticut 66.4% D Blumenthal55.2% D Delaware(special) Appointed Coons56.6% D Florida Appointed Rubio48.9% R Georgia 57.9% R Isakson58.3% R Hawaii 75.5% D Inouye74.8% D Idaho 99.2% R Crapo71.2% R Illinois Appointed Kirk48.0% R Indiana 61.7% D Coats54.6% R Iowa 70.2% R Grassley64.4% R Kansas 69.9% R Moran70.1% R Kentucky 50.7% R Paul55.7% R Louisiana 51.0% R Vitter56.6% R Massachusetts(special) Appointed Brown51.6% R Maryland 64.8% D Mikulski62.2% D Missouri 56.1% R Blunt54.2% R Nevada 61.0% D Reid50.3% D New Hampshire 66.2% R Ayotte60.1% R New York(regular) 71.2% D Schumer66.3% D New York(special) Appointed Gillibrand63.0% D North Carolina 51.6% R Burr54.8% R North Dakota 68.3% D Hoeven76.1% R Ohio 63.9% R Portman56.8% R Oklahoma 52.8% R Coburn70.6% R Oregon 63.4% D Wyden57.2% D Pennsylvania 52.6% R Toomey51.0% R South Carolina 53.7% R DeMint61.5% R South Dakota 60.6% R Thune100.0% R Utah 68.6% R Lee61.6% R Vermont 70.6% D Leahy64.4% D Washington 55.0% D Murray52.4% West Virginia(special) Appointed Manchin 53.5% Wisconsin 55.3% D Johnson51.6% R

Gains and losses

Retirements Three Democrats and six Republicans retired rather than seek re-election. Three Democrats retired rather than seek election to finish the unexpired term and one Democrat retired rather than seek election to finish the unexpired term and election to a full term. StateSenator Age at end of term AssumedofficeReplaced by Connecticut 66 1981 Delaware (special) 71 2009 Florida 41 2009 Illinois 73 2009 Indiana 55 1999 Kansas 54 1996 Kentucky 79 1999 Massachusetts (special) 72 2009 Missouri 71 1987 New Hampshire 63 1993 North Dakota 68 1992 Ohio 75 1999 West Virginia (special) 36 2010

Defeats Three Democrats and one Republican sought re-election but lost in either the primary or general election.

StateSenatorAge atend of termAssumedofficeReplaced by Arkansas 50 1999 Pennsylvania 80 1981 Utah 77 1993 Wisconsin 57 1993

Post-election changes One Republican resigned on May 3, 2011, and was replaced by an appointee.

StateSenatorReplaced by Nevada(Class 1)

Race summary

Special elections during the 111th Congress In these special elections, the winner was seated in the fall of 2010 (excluding Massachusetts), once they qualified and their elections were certified. Sorted by election date, then state, then class.

State Incumbent Result Candidates Senator Party Electoral history Massachusetts(Class 1) 2009 Interim appointee ineligible to run.New senator elected January 19, 2010 and seated February 4, 2010.Republican gain. Delaware(Class 2) 2009 Interim appointee retired.New senator elected November 2, 2010 and seated November 15, 2010.Democratic hold. Illinois(Class 3) 2009 Interim appointee retired.New senator elected November 2, 2010 and seated November 29, 2010.Winner also elected to next term; see below.Republican gain. New York(Class 1) 2009 Interim appointee elected November 2, 2010. West Virginia(Class 1) 2010 Interim appointee retired.New senator elected November 2, 2010 and seated November 15, 2010.Democratic hold.

Elections leading to the next Congress

In these regular elections, the winners were elected for the term beginning January 3, 2011; ordered by state.

All of the elections involved the Class 3 seats.

State Incumbent Result Candidates Senator Party Electoral history Alabama 1986199219982004 Incumbent re-elected. Alaska 2004 Incumbent lost renomination, but was re-elected as a write-in candidate. Arizona 1986199219982004 Incumbent re-elected. Arkansas 19982004 Incumbent lost re-election.Republican gain. California 199219982004 Incumbent re-elected. Colorado Interim appointee elected. Connecticut 19801986199219982004 Incumbent retired.Democratic hold. Florida Interim appointee retired.Republican hold. Georgia 2004 Incumbent re-elected. Hawaii 19621968197419801986199219982004 Incumbent re-elected. Idaho 19982004 Incumbent re-elected. Illinois Interim appointee retired.Kirk was also elected to finish the previous term; see above.Republican gain. Indiana 19982004 Incumbent retired.Republican gain. Iowa 19801986199219982004 Incumbent re-elected. Kansas 1996 19982004 Incumbent retired to run for Governor of Kansas.Republican hold. Kentucky 19982004 Incumbent retired.Republican hold. Louisiana 2004 Incumbent re-elected. Maryland 1986199219982004 Incumbent re-elected. Missouri 1986199219982004 Incumbent retired.Republican hold. Nevada 1986199219982004 Incumbent re-elected. New Hampshire 199219982004 Incumbent retired.Republican hold. New York 19982004 Incumbent re-elected. North Carolina 2004 Incumbent re-elected. North Dakota Democratic-NPL 199219982004 Incumbent retired.Republican gain. Ohio 19982004 Incumbent retired.Republican hold. Oklahoma 2004 Incumbent re-elected. Oregon 1996 19982004 Incumbent re-elected. Pennsylvania 19801986199219982004 Incumbent lost renomination.Republican gain. South Carolina 2004 Incumbent re-elected. South Dakota 2004 Incumbent re-elected. Utah 199219982004 Incumbent lost renomination.Republican hold. Vermont 197419801986199219982004 Incumbent re-elected. Washington 199219982004 Incumbent re-elected. Wisconsin 199219982004 Incumbent lost re-election.Republican gain.

Closest races Seven November races, as well as the Massachusetts special election in January, had margins less than 10%: District Winner Margin Illinois Republican (flip) 1.6% Colorado Democratic 1.7% Pennsylvania Republican (flip) 2.0% Alaska Republican 4.0% Washington Democratic 4.7% Massachusetts Republican (flip) 4.8% Wisconsin Republican (flip) 4.8% Nevada Democratic 5.7%

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

Alabama

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."

Alaska

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 in the Republican primary.

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

Arizona