3D Chess. On the fence lefties think he'll pack it but doesn't want to piss off the on the fence righties. On the fence rightites think he won't pack it but doesn't want to piss off the on the fence lefties.
He won't, only Congress can and the numbers have been between five and ten. Politics aside, there is too much evidence of supes interpreting the law to their bias. A protracted period of they ruling against the majority will of the populace is a very bad thing.