The Post is really kicking butt on the Kennedy beat lately. Today they bring us the tale of — you will never believe this — a branch of the iconic clan that is dealing with family problems involving accusations of infidelity and alcohol! Bobby Kennedy Jr., son of RFK, is having marital issues with wife Mary Richardson Kennedy — troubles that bubbled to the surface on May 15 when Mary drove the family car into a curb at a Westchester County Catholic school carnival and was arrested for driving under the influence. “It’s no big surprise that she’s drinking. She has problems, and in the past couple of years — certainly the last year — it’s gotten worse,” a source told the tabloid, explaining that she suspects her husband has cheated on her. The couple apparently has had several encounters with local cops, including one time in 2007 when Bobby tried to drive Mary to see a shrink at a local hospital and she bolted from the car, trying to escape. According to the Westchester Journal News, he had to take her down in the middle of the road and hold her to prevent her from hurting herself. Not pretty. Grand Jackie would not have approved.