Marco Rubio is up for re-election, but I think it will be no contest, since Ron DeSantis is up for re-election as Governor. I think Wisconsin will be in the R and Pennsylvania, if the get someone with a backbone who will be a strong Conservative,, will keep PA in the GOP. Now NV, GA and AZ could flip to the R... maybe a few others too...
In 2018 Lou Barletta, a strong Conservative, ran against democrat Bob Casey Jr. Casey won with 56% of the votes to Barletta's 43%.
In 2022, the RINO PA Senator Toomey will not seek reelection. If the RNC and PA-RC cannot stop Philly and Pittsburgh cheating and they run another incompetent Senate campaign in 2022, PA will have 2 dem senators.
The sad fact is that 2020 showed the PA republican controlled state legislature is impotent in stopping dem cheating.