[Gov. Janet] Mills, who is 78, is trying to dislodge Susan Collins, a spring chicken at 73, in Maine’s Senate race this fall. Unlike her Democratic primary opponent, the gun-loving ex-Marine turned oyster farmer Graham Platner, Mills does not have a dicey Reddit history or a recently covered-over Nazi tattoo. She is well-known in the state and has a tested political organization. And yet, in several recent polls, she has been trailing Platner.