How many Republican held US Senate seats Democrats need to win to get back in the majority in 2020?
Democrats need a net gain of 4 seats to get back in the majority.
Democrats are going to lose VT(Sanders-D) when Sanders leaves the US Senate to become the next POTUS. The appointed Republican VT US Senator is going to be the underdog in the 2021 special election.
Democrats will also lose AL(Jones-D) who is going to lose to any of the Republican candidates except Moore-R.
Democrats will need to win 6 Republican held US Senate seats to get back in the majority.
1)CO(Gardner-R)Hickenlooper-D
2)AZ special(McSally-R)Kelly-D
3)NC(Tillis-R)Cunningham-D
4)ME(Collins-R)Gideon-D
5)IA(Ernst-R)Greenfield-D
5/6) GA regular(Perdue-R)Tomlinson-D and/or GA special(Loeffler-R)/Warnock-D.
If 2020 is a strong Democratic wave election year, Democrats could win-
KS(OPEN Roberts-R)Bollier-D if Kobach-R is the Republican Nominee.
KY(McConnell-R)McGrath-D
MS(Hyde Smith-R)Espy-D
SC(Graham-R)Harrison-D
TX(Cornyn-R)Hegar-D