He's dropping him back to his NYC days as tabloid fodder and reality show star. A person at a B/C celebrity level.
Typically, before norms and decorum went into the wastebasket, a former President would be given some kind of deference. We don't have a modern precedent really of a former President running again to know for sure but I suspect if Jimmy Carter or George HW Bush ran again, they'd be called Mr. Carter or Mr. Bush, if not "The former President" by their primary opponents. Maybe not.