MADISON, Wis. (AP) — House Speaker Paul Ryan’s Republican primary challenger told a columnist for the New York Post in a Twitter message to “Eat a bullet.”

Paul Nehlen, who has built a reputation as a firebrand conservative backer of President Donald Trump, sent the tweet on Wednesday night. It came after a back and forth with Post columnist John Podhoretz that stemmed from a tweet Nehlen sent about a bill passed by the House that would make it easier for gun owners to legally carry concealed weapons across state lines.

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Podhoretz tweeted to Nehlen: “Maybe you should eat something. Your brain needs nourishment. It’s the size of a pea.”

Nehlen tweeted in response: “Do us all a favor, Podhoretz. Eat a bullet.”

Nehlen posted a follow up message Thursday suggesting his comment was a joke. He tweeted an advertisement for a Dutch snack food called “Boston Bullet.”

Podhoretz did not immediately reply to a message seeking comment Thursday. Ryan’s campaign spokesman, Kevin Seifert, dismissed the tweets as “the latest embarrassing controversy that Paul Nehlen has created for himself.”

Ryan easily defeated Nehlen in the 2016 primary, securing 84 percent of the vote.