In recent months, Mr. Sayoc’s behavior changed. His posts took on a darker, more obsessive tone, often accompanied by threats of violence and gory images of bloody animal carcasses. No longer mistakable as an everyday internet partisan, he posted repeatedly about “unconquered Seminoles,” a reference to the tribe that he appears to have adopted. (It also appeared on his van.) And on Twitter, his messages turned dark and sinister.
He directed a tweet at Ms. Waters, the California Democrat, with a photo of what appeared to be her house. The message read: “see you soon.”
He sent another to Eric H. Holder Jr., an attorney general under Mr. Obama, that read, “See u soon Tick Tock.” And he told Zephyr Teachout, a Democrat who ran unsuccessfully for attorney general in New York, that he had a surprise waiting for her. “We Unconquered Seminole Tribe have a special Air boat tour lined up for you here in our Swamp Everglades,” he wrote. “See u real soon. Hug your loved ones.”