Democratic Senatorial Campaign Committee

This result may be attributed to George W. Bush's post-9/11 popularity and the death of Senator Paul Wellstone of Minnesota, who had been favored to win.

The defection of Republican Arlen Specter of Pennsylvania in April 2009 and the swearing-in of Al Franken in July 2009 brought the balance to 60–40.

[8] Because this is not easy to do in a presidential election year, the DSCC had gone very much on the offensive, depicting Republican candidates and donors, and especially the Tea Party, as extreme.

The Democrats would have been able to retain a majority with 48 seats (assuming the two Independents continued to caucus with them) because, in event of a tie vote, Vice President Joe Biden becomes the tie-breaker.

The party held all three competitive Republican-held seats (Kentucky, Kansas, and Georgia), and defeated incumbent Democrats in North Carolina, Colorado, and Arkansas.

In the process of taking control of the Senate, Republicans defeated three incumbent Democrats, a task the party had not accomplished since the 1980 election.

Incumbent Virginia Democrat Mark Warner was declared the winner of his race by a narrow margin over Republican Ed Gillespie on November 7, and Alaska Republican Dan Sullivan was declared the winner against Democratic incumbent Mark Begich a week later, on November 12.

Seven of the Republican seats that were up for reelection were in states that Obama won twice, Mark Kirk of Illinois, Pat Toomey of Pennsylvania, Ron Johnson of Wisconsin, Kelly Ayotte of New Hampshire, Chuck Grassley of Iowa, Rob Portman of Ohio and Marco Rubio of Florida who ran for reelection after an unsuccessful presidential bid.

There were several other states the Democrats were focused on where the Republican incumbents may have been vulnerable: John McCain of Arizona, Lisa Murkowski of Alaska, John Boozman of Arkansas, Richard Burr of North Carolina, Johnny Isakson of Georgia, Roy Blunt of Missouri, Rand Paul of Kentucky who simultaneously ran for president, and Senator David Vitter of Louisiana.

For the first time the DSCC did not endorse a candidate in the general election in California because both women were Democrats competing for the seat of retiring Senator Barbara Boxer.

The unusually imbalanced 2018 Senate map, created by successful 2006 and 2012 elections, resulted in a large number of vulnerable Democrats.

First-term Senator Catherine Cortez Masto of Nevada chaired the DSCC for the 2019-2020 election cycle, the first Latina to do so.

In Michigan, Senator Gary Peters faced a very strong Republican candidate, businessman John James, but was nevertheless expected to win.

Colorado was seen as the most likely flip for the Democrats, due to incumbent Senator Cory Gardner tying himself heavily to Trump in a state he had lost by 4.5 points in 2016, and expected to lose by a much larger margin this cycle.

Republicans needed to defend seats in key swing states such as Arizona, Georgia, North Carolina, and Iowa.

Seats in South Carolina, Kansas, Montana, and Alaska became surprisingly competitive, compared to their usual Republican lean.

North Carolina was seen as a highly likely flip, until the Democratic nominee, Cal Cunningham, got involved in a sex scandal that significantly hurt his candidacy.

Democrats flipped both seats, allowing them to take control of the Senate, since Vice President Kamala Harris would cast the tie-breaking vote.

In order to maintain their majority in the Senate, Democrats had to defend Catherine Cortez Masto in Nevada, Raphael Warnock in Georgia, Mark Kelly in Arizona, and Maggie Hassan in New Hampshire, all of which represented states that incumbent President Biden had won in 2020.

Senator Gary Peters of Michigan was selected as DSCC chair for a second consecutive cycle, the first since Chuck Schumer to be so.

With Manchin retiring, the West Virginia seat was written off, putting focus on Jacky Rosen in Nevada, Bob Casey Jr. in Pennsylvania, Tammy Baldwin in Wisconsin, newcomers Ruben Gallego in Arizona and Elissa Slotkin in Michigan; all these were hotly contested swing states in 2020.

The entry of Larry Hogan into Maryland's race was an unexpected turn that is expected to siphon funds from tougher fights.

Tester's 12-point and Brown's 5-point edge were not enough to win in their deep-red states, with Florida and Texas's rightward shift clearly putting Democratic Senate hopes away.