President Joe Biden challenged Democrats who wish to oust him from his party’s nomination on MSNBC’s Morning Joe on Monday, saying: “Any of these guys that don’t think I should run, run against me. Announce for president. Challenge me at the convention.”

Biden made the remark as part of a fiery call-in to the program, shortly after he released a letter firmly stating he will not drop out of the presidential race, and mocked those who challenged him previously.