Secret Service Director Mark Sullivan announced his retirement Friday, bringing to a close a turbulent period for the law enforcement agency. Part of his work he accomplished included a South American prostitution scandal and a pair of White House gate-crashers. Sullivan was director for nearly 7 years. During this time,  he had to answer serious questions from lawmakers on two occasions about his employees' actions on the job and off. Sullivan's retirement is effective Feb. 22. His replacement has not been announced.