During the 2006 and 2008 US Senate Election cycle Democrats gained a total of 14 seats,
2006
PA- Casey-D
OH- Brown-D
RI-Whitehouse-D
MO-McCaskill-D
MT-Tester-D
VA- Webb-D
2008
VA-Warner-D
NM-Udall-D
CO-Udall-D
NH-Shaheen-D
NC-Hagan-D
OR-Merkley-D
AK-Begich-D
MN-Franken-D
Democrats could gain a total of 14 seats during the 2018 and 2020 US Senate Election cycle if Democrats
2018
Hold onto Democratic held seats in Trump 2016 States- FL-Nelson-D,IN-Donnelly-D,MI-Stabenow-D,MO-McCaskill-D,MT-Tester-D,ND-Heitkamp-D,OH-Brown-D,PA-Casey-D,WV-Manchin-D,and WI-Baldwin-D and pick up AZ-Sinema-D,NV-Rosen-D,TN-Bredesen-D,and TX-O'Rourke-D.
2020
Hold onto AL-Jones-D, the only Democratic held seat from a Trump 2020 state. Democrats will carry MI-Peters-D in the 2020 US Presidential Election.
Pick up
1)AZ- Gallego-D
2)CO- Johnston-D
3)GA- Tomlinson-D
4)IA- Pritchard-D
5)KY- Overly-D
6)LA- Mitch Landrieu-D
7)ME- Cote-D
8)MS- Presley-D
10)NC- Foxx-D