In the tweet, which was deleted by Friday morning, state Rep. Briscoe Cain (R) wrote: “My AR is ready for you Robert Francis.” O'Rourke's birth name is Robert Francis O'Rourke.
A spokesperson for O'Rourke told The Guardian that his campaign reported the post to the FBI.
Cain’s tweet came in response to another post shared from O’Rourke’s account on Thursday that quoted remarks he made during the debate in Houston when he declared, "Hell yes, we’re going to take your AR-15."
O’Rourke took issue with Cain's tweet, calling it a “death threat.”
“Clearly, you shouldn't own an AR-15—and neither should anyone else,” O’Rourke added.
Cain fired back at O’Rourke in a tweet around midnight, in which he called the Democrat "a child."
The state legislator also lashed out at a social media user who asked him if he intended to threaten O’Rourke with the tweet, saying: “You’re an idiot.”