They're ba-aack. Bill Clinton and George H. W. Bush, America's political odd couple, are teaming up for another big roadshow, this time to raise money for victims of Hurricane Katrina. Last week, they stood shoulder to shoulder with President George W. Bush in the Oval Office, the 59-year-old Clinton now completely gray and looking a bit fragile, and the 81-year-old Bush looking stooped and a bit weary. Later the pair appeared together in Houston, chatting with evacuees at the Astrodome and the Reliant Center Arena. Their goal was to demonstrate unity at a time of calamity.