WASHINGTON – ...But in the brave new world of YouTube politics, almost anything is possible. And just 18 months after its launch, the website is already playing an integral role in campaigns. ..."We've always known the power of video, but now everybody in the world with a cellphone or a small high-res camera and broadband" can get in the act, says Michael Cornfield, an expert on the Internet and politics who teaches at George Washington University. "YouTube is the last link in the system, which is, now 'I can go find it.' " For several years, political advisers have been...