Hoping to blunt the impact of an expected torrent of negative campaigning, the presidential campaign of presumptive Democratic nominee Barack Obama has launched a Web site dedicated to dispelling rumors and myths about him. Obama’s campaign launched a site it calls “FightTheSmears” on Thursday, posting several so-called smears taken from various media sources and juxtaposing those rumors with what it says is the truth. In addition to being a way to rebut rumor and innuendo, the site is also designed to use social media to spread the word about Obama.