CHICAGO (AP) -- A veteran Illinois state senator was arrested Wednesday after allegedly trying to board a flight from Chicago to Washington with a gun and ammunition in a carry-on bag, authorities said.

Sen. Donne Trotter, a Chicago Democrat who recently announced he would run to replace Jesse Jackson Jr. in the U.S. House, was carrying an unloaded .25-caliber Beretta handgun and a magazine clip with six bullets when he tried to board a flight at O'Hare International Airport, according to Chicago police.

Trotter, who is part the Illinois Senate's Democratic leadership, was charged with a felony.

The gun and clip were found in an outside zippered pocket of Trotter's garment bag during routine X-ray screening, according to a Chicago police report.

Trotter told Transportation Security Administration officers that he uses the weapon for work as a security officer at a Chicago security and detective firm. He said he worked late Tuesday night and did not realize the weapon was in the bag when he packed for his Wednesday morning flight, the police report said.

Messages left by The Associated Press for Trotter on his cellphone and at his office in Chicago were not immediately returned.

Trotter, 62, was charged with a Class 4 felony, which carries a penalty of one to three years in prison upon conviction. He was expected to appear in Cook County bond court Thursday, Cook County State's Attorney's office spokeswoman Tandra Simonton said.

Police said Trotter would spend Wednesday night in a police lockup.

Trotter is licensed to carry a weapon and has a Firearm Owner's Identification card, Chicago police spokeswoman Melissa Stratton said.

Trotter was carrying a "firearm control card," issued by the Illinois Department of Financial and Professional Regulation, that allows him to carry a weapon during work hours and for no more than an hour commuting to or from work. A department spokeswoman said a security company helped Trotter obtain the card.

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The card is issued after completion of 20 hours of classroom firearm instruction and 20 hours of firearm handling training.

Trotter — known for wearing bowties and sometimes riding his motorcycle to Springfield — served in the Illinois House from 1988 to 1993, and since then in the Illinois Senate, where he chairs the Democratic majority caucus.

Under former Senate President Emil Jones, he was the Senate Democrats' budget negotiator and known as a cool, calm presence in the often-contentious budget debates during the tenure of ex-Gov. Rod Blagojevich, who is now imprisoned on corruption charges.

Trotter previously ran for Congress in 2000, a race in which both he and then-state Sen. Barack Obama lost to U.S. Rep. Bobby Rush.

He was born in Cairo, in far southern Illinois, earned an undergraduate degree from Chicago State University and a law degree from Loyola University. He is married and has four children.