Koster championed legislation for Truth in the Missouri Court System, and proposed a bill (SB55) that aimed to eliminate paternity fraud. On August 1, 2007, Koster made Missouri political history when he announced that he was leaving the Missouri Republican Party to become a Democrat. Citing his longstanding differences with the Republican Party on issues like stem cell research, workers' rights, and the non-partisan court plan, Koster said that the Missouri Republican Party had become too beholden to the extreme right-wing to lead the state of Missouri. He said, "Today, Republican moderates are all but extinct."