Bob Arnold is the corrupt, former congressman for Springfield's State. At first, he seemed like a decent guy, as evidenced by Moe and Barney's opinion of him, and even Lisa's. However, prior to Lisa's first encounter with him, he was talking to a lobbyist representing the Timber Company about tearing down Springfield Forest, and was about to accept it, but decided to try and postpone it and meet somewhere secret when Lisa and her family arrived. He later meets with the Timber lobbyist at the Winifred Beecher Howe museum exhibit (as it was allegedly the least likely place someone would stumble on the meeting). When asked on his standing, he accepted the bribe (or, as he answered it, "let me put it this way: Timbeeeeerrrrrrr!!"). However, Lisa also happened to be at the exhibit admiring it when she witnessed the whole bribe. After witnessing it, she decided to make a new essay that condemns democracy and exposes Bob Arnold's accepting the bribe. Thanks to the inflammatory essay, the FBI quickly caught wind of his activities. He was arrested for accepting a bribe to allow oil drilling on President Roosevelt's head on Mount Rushmore in a sting operation, and was expelled from Congress. His arrest brought back Lisa's faith in the system. According to the Washington Beacon, he had become a born-again Christian shortly after being removed from office. He would have worked with the late Horace Wilcox as a fellow congressman for Springfield's State.
Congressman Arnold's first meeting with Lisa showed he had much political savvy and social graces, as he charms Lisa by saying one day she may grow up to be a Congresswoman and commends Lisa for correctly stating how many women were Members of Congress. He gets photographs taken of himself with Lisa, which get put into Springfield newspapers and are all that is needed to convince Barney and Moe that he is a decent man worthy of reelection, which serves to show the ease Congressman have in convincing voters to keep reelecting them (or at least Moe & Barney). Other than the logging bribe and the failed Roosevelt Oil bribe, it's implied that he may have accepted a bribe to bury toxic waste during the meeting with the Timber lobbyist. Also, he may be somewhat of a womanizer, as he said "Look, what a pooch" in regards to Winifred Beecher Howe's statue.