The following year, Harmon left the show after three seasons (with Abbie Carmichael written off as being called on to serve the U.S. Attorney's office) and was replaced by Elisabeth Röhm as Assistant District Attorney Serena Southerlyn. The year after that, Wiest left the show after two seasons and was replaced by retiring U.S. Senator Fred Thompson as District Attorney Arthur Branch, whose character was conceived of as being much more right-leaning than his predecessors in the DA's office, and was a direct reaction to the September 11 attacks. No mention was made on the show of what happened to Nora Lewin, though producers said her character was only supposed to be an interim DA.