[albedoa]

There's a style choice. I prefer: Bernie Sanders's

We can agree that the title is clearly wrong :D (In case it gets fixed, the title was submitted with: Sander's)

[raldi]

Actually, if you want to get technical, it should be "Bernies Sander".

[Someone1234]

No, because that's not his name. His name is Bernard Sanders and he goes by "Bernie." So Bernie Sanders, or expanded out to Sanders's or Sanders' are correct.

[keeganpoppen]

Bernie Sanders's'

[yellowapple]

Bernie S'anders.