The weapon, presumably left behind in the bathroom by accident, was discovered by a CBS News/National Journal reporter, who alerted a flight attendant about the gun. A member of the Secret Service on board the plane was informed and retrieved the gun.
Romney has traveled with Secret Service protection since early February and has an armed detail assigned to him at all times. His wife, Ann, was just assigned her own detail - albeit a smaller one - last Friday.
Secret Service spokesman Ed Donovan told CBS News/National Journal in a statement: "We are aware of the incident. We take the care and custody of our equipment, especially firearms, very seriously. We will deal with this matter internally and in an appropriate manner."