The gun was found by TSA agents in Trotter's carry-on bag at around 7 a.m. on Dec. 5 while the state senator was going through security at Chicago's O'Hare International Airport. Trotter said he forgot that he left the gun in his carry-on bag. 

Despite the charge, Trotter had initially said he would continue to run for the seat in Illinois's heavily Democratic 2nd District. He was considered by many to be one of the stronger contenders for the seat, but he faced a wide Democratic primary slate of at least six other local Democrats vying for the seat.

Trotter's exit still leaves former Rep. Debbie Halvorson, state Sen. Toi Hutchinson, Cook County Chief Administrative Officer Robin Kelly, former NFL linebacker Napoleon Harris, Alderman Anthony Beale and former Rep. Mel Reynolds in the running.