It is a cast worthy of a political thriller: a former convict whose claims about a former president and first lady spurred a criminal investigation; a prominent senator's brother-in-law, who worked undercover for federal agents looking into the case; political enemies of the former first family trying to dig up fresh dirt; and some of Hollywood's biggest stars. All these characters will share some of the spotlight beginning Tuesday in a Los Angeles courtroom, where David F. Rosen, the former fund-raising director for Senator Hillary Rodham Clinton, will go on trial on charges that he illegally underreported the cost of...