There are 12 Democratic and 21 Republican Senate seats on the ballot this November. The math is usually on the side of the party with the fewer seats to defend and this November, the math is with the Democrats.
However, several, but not all, of the Republicans running for re-election are running from states that Donald Trump comfortably carried in 2016 – exceptions include Martha McSally (R-AZ), Susan Collins (R-ME), Cory Gardner (R-CO) and Thom Tillis (R-NC). Only one Democrat, Doug Jones (D-AL), is running for re-election in a state that Trump overwhelmingly carried Alabama by 27.7% and is considered to be the most vulnerable Democrat running this November.
There are also some Senate seats that may be on the political bubble for one reason or another including Mitch McConnell (R-KT), Lindsey Graham (R-SC), Joni Ernst (R-IA), Dan Sullivan (R-AK), and two seats in Georgia.
ALASKA: AL GROSS (D) VS. DAN SULLIVAN (R)
ARIZONA: MARK KELLY (D) VS. SEN. MARTHA MCSALLY (R)
COLORADO: JOHN HICKENLOOPER (D) VS. SEN. CORY GARDNER (R)
GEORGIA: TBD (D) VS. SEN. KELLY LOEFFLER (R)
IOWA: THERESA GREENFIELD (D) VS. JONI ERNST (R)
KANSAS: BARBARA BOLLIER (D) VS. KRIS KOBACH (R)
KENTUCKY: AMY MCGRATH (D) VS. KRIS KOBACH (R)
MAINE: SARA GIDEON (D) VS. SUSAN COLLINS (R)
MONTANA: STEVE BULLOCK (D) VS. STEVE DAINES (R)
NORTH CAROLINA: CAL CUNNINGHAM (D) VS. TOM TILLIS (R)
SOUTH CAROLINA: JAIME HARRISON (D) VS. LINDSEY GRAHAM (R)
TEXAS: MJ HEGAR (D) VS. JOHN CORNYN (R)