You see, the population had developed a sense of Bigotry Entitlement. Once that had been officially sanctioned, the populace were not particularly interested in obeying subsequent emperors (at least not until Christianity became the “official” religion of the Empire in the fourth century) who were telling them to ease up on their acts of violence. The absence of dog whistles does not then disperse the dogs!
Marcellus and Valerian were killed for being Christians during a time when leaders in Rome were calling for decency and an end to violence–not during an active, state-sanctioned persecution.
This means that the current regime in Washington, DC, is even more dangerous than what it might do during its tenure. Yes, it can be held in check by the 2018 midterms; it can even be voted out in 2020. The regime can be followed by a kind-hearted, diversity-loving, and tolerant administration with a policy of acceptance and respect for all persons. But that does nothing at all to ensure that the Hatred Genie has dissipated or that the dogs will disperse.
Just ask the families of Marcellus and Valerian.