1. Feinstein (D) of California will not be running. Last election, she won with 54-percent. Lot of frustration in the state, and suggestions that the Governor might be the one running for the Democratic Party.
2. Florida's Rick Scott (R) is the incumbent (50.1-percent in last election). He'll run again, and have a fair amount of competition.
3. Michigan's Debbie Stabenow (D) marginally won last time (52-percent) and intends to run again. Will have some competition this time around.
4. Montana's Jon Tester (D) won the election (3rd time) in 2018 with 50.3-percent. Stiff election this time around.
5. Nevada's Jacky Rosen (D) won 2018 with 50.4-percent. Stiff competition this time.
6.. Vermont's Bernie Saunders (I) is currently age 80 and I have doubts he'll run again. Wide open race if he declines. Entirely possible that a Green Mountain Peace and Justice Party candidate might attract votes to win.
7. West Virginia's Joe Manchin is up for re-election.
8. Texas's Ted Cruz and Utah's Mitt Romney will be up for re-election (both R). Neither has said if they will run again.
9. Virginia Tim Kane (D) is up for re-election and hasn't said if he'll run (marginally won last time).
Odds here? I expect a minimum of two Republican lost seats, but the Democrats might potentially lose four (including some weird replacement for Bernie).
On Bernie and Vermont....things are weird enough that alternative rock singer 'Trey' Anastasio III could put his name out there and probably get 50-percent of the vote.....strictly on the fact that half of Vermont claim him as a 3rd-cousin.
As much as everyone is looking at 2022's mid-term for changes in the Senate....I'd say 2024 has the same impact.