2 max.
Stevens and Ginsberg for age & health reasons.
Breyer is a 71 year old Clinton appointee. I have no reason to question his health or fitness, but the opportunity to step down with a liberal doing the appointing and a huge dem majority in the Senate might be very attractive to him and his party.
If they could get 3 40-something liberals on the bench, they’d lock down 3 liberal seats for decades. It would be tempting for the libs to have a “come to Jesus meeting” with Justice Breyer.