Sometimes, like a Cinderella team marching through March, Sen. Barack Obama's presidential campaign seems nothing short of charmed. It helps that while Sen. Hillary Rodham Clinton has 10 weeks to make Obama totally and entirely unelectable, Obama just has to wait out the clock. But the outside help Obama is getting (some that he asked for, some that he didn't) is the X-factor -- and it means that, even as Obama grapples with perhaps the biggest challenge to his candidacy, he will be the nominee short of something else dramatic happening in the race that's already seen everything. To survey...