15 Democratic Senators are from states with Republican governors.
4 of them aren’t an issue as, by state law, replacements must be of the same party: AZ (Sinema-Kelly) and MD (Cardin-Van Hollen).
That leaves 11 senators who could be replaced by a republican if anything happens to them. 6 of them are also over 70, (age shown)
- GA: Warnock, Ossoff
- MA: Warren-71, Markey-74
- MT: Tester
- NH: Shaheen-73, Hassan
- OH: Brown
- VT: Leahy-80, Sanders-79
- WV: Manchin-73