I don’t know the answer to the question in the title, but thought to post a list of the 34 Senate races in 2020 here to help visualize exactly what’s needed to get to 50.
Democrat, sure thing, all popular incumbents
DE Coons
IL Durbin
MA Markey
NJ Booker – if Booker runs for higher office, will Ds still have a lock?
OR Merkley
RI Reed
Democrat incumbent, victory most probable
NH Shaheen
NM (Udall retiring)
VA Warner
MI Peters - first-termer in danger?
MN Smith - first-termer in danger?
Two seats occupied by Rs whom Ds may be favored to upset.
AZ McSally (unelected) – Mark Kelly plans to run against her. Must win for the Ds!
CO Gardner (1st term) – who should Ds run against him?
To win 50 seats the Ds need to win all the above races AND two (2) from The critical Eleven races, shown in pink. I’ve tried to sort them very roughly by decreasing likelihood of D victory.
If AZ or CO is lost, the D’s need 3 seats from the following sub-list of 11, but the D’s are underdogs in each case.
NC Tillis
ME Collins (has the popular woman sullied herself by embracing right-wing lies and hatreds?)
GA Perdue – is Abrams the only one who can beat him?
AL [Jones – see note below]
IA Ernst
KS Roberts, retiring
MS Hyde-Smith
KY McConnell
TX Cornyn – could Beto beat him?
MT Daines
TN Alexander, retiring
Republican, sure thing, almost all popular incumbents
AK Sullivan
AR Cotton
ID Risch
LA Cassidy
NE Sasse
OK Inhofe
SC Graham
SD Rounds
WV Capito
WY open?
To make the seat counting more straightforward, the Alabama seat should be counted as Republican:
[SPOILER] As a lark, spurred by their hero announcing he could kill in broad daylight and still get elected, the Rs ran a child molester for a two-year Senate seat. The D got a whopping 18% of the white evangelical vote! While 80% of the white evangelicals held firm and came out in favor of child molestation this wasn’t enough to beat the moral vote. Having learned their lesson, the evangelicals will probably nominate a scumbag who only hits on girls 16+, thus reclaiming their Senate seat.
Sure, we’d like to dream of an Alabama where Jones wins re-election, but for the purpose of the list, Jones is the one incumbent Senator heavily favored NOT to win re-election.[/SPOILER]