POTUS was referring to the people Sessions was supposed to be investigating, not Sessions.
Definition of pecking order
1: the basic pattern of social organization within a flock of poultry in which each bird pecks another lower in the scale without fear of retaliation and submits to pecking by one of higher rank
broadly : a dominance hierarchy in a group of social animals
2: a social hierarchy
Sorry, but all the evidence is on the side of "stable genius."