A warrant has been issued for Mr. Vandevere, 52, who had not been arrested as of Monday night, according to the United States Attorney’s Office for the district. He could not be reached on Monday evening, and it was unclear whether he had a lawyer.

The account from which the threat was posted has been suspended. A Twitter spokesman said the company would not comment on individual accounts for privacy and security reasons.

Mr. Rashid, who moved to the United States from Pakistan with his family in 1987, had seen threatening language like that before. “I don’t know if my experience is necessarily unique,” he said. “As a person of color, as an immigrant and as a Muslim, to speak publicly about your faith and to receive death threats is not uncommon.”

According to a screenshot of the tweet, which Mr. Rashid shared on his own account, the threat included the words “Muslim scum” and showed a black-and-white picture of a man hanging by a rope. (That man appeared to be Leo Frank, a Jewish factory manager who was lynched by a mob in Georgia in 1915. According to the Library of Congress, his case is “widely regarded as a flash point of anti-Semitism” in the United States.)

Last month, Mr. Rashid won the Democratic primary for the District 28 seat in the State Senate. In November, he will challenge Richard Stuart, the Republican incumbent, who was first elected in 2007. Mr. Rashid is campaigning on a range of issues including passing the Equal Rights Amendment, expanding health care access, reforming criminal justice and increasing education funding.