Powerthief needs to start wagons to maximize their power. Once the wagon picks up, the PT can choose to use their power. If the wagon pressure causes the target to claim, the PT is primed to steal the power if the mislynch goes through.
Of note, Jamie has started wagons on:
Brain (vote stealer)
Flash (no claim)
Me (no claim)
Moscow (no claim at the time)
damo (either no claim at the time or mammal)
I think Jamie is scum. If he's scum, I think he's the powerthief.