What is or is not relevant for judging Senator Sessions’s (yes, it is "s's") likely performance as Attorney General? Presumably, his current behavioral characteristics and abilities. What if some of his past behavioral characteristics and abilities were not suitable for an Attorney General? They are relevant only if they are current.
Example: Some people claim that Sessions is a racist, based on remarks made long ago. Has he exhibited any behavior that would suggest that he is a racist now? If not, his past remarks are irrelevant. Are the people who say Sessions is a racist failing to distinguish the present tense from the past tense or are they irrational?
Presumably, it is a good idea to have people learn new good behavior that replaces bad behavior. New good behavior is established by positive reinforcement. Punishing past bad behavior after it has disappeared from a person’s repertoire is counterproductive.
A point to ponder: Consider a person who commits a heinous crime and is sentenced to death. Suppose, by magic if you wish, the person is transformed into an ordinary person with no tendency to unacceptable behavior. What is the rational course of action, to execute him or release him? The latter, of course.