The billionaire's new job raises tricky First Amendment questions, with implications for public health, says Ari Cohn.

"Overall, the long-term increase in hate speech and the prevalence of potentially inauthentic accounts are concerning, as these factors can undermine safe and democratic online environments and increase the risk of offline harms," the study said

The number of posts containing slurs doubled and the number of bot accounts also increased, new research by a California team suggests.