Today on the presidential campaign trail (AP)

Republican presidential candidate US Sen. John McCain, seen here on July 29, 2008, invoked gossip-page perennials Britney Spears and Paris Hilton Wednesday to portray Democrat Barack Obama as a vapid celebrity who was unfit to lead.(AFP/Getty Images/Max Whittaker)AP - McCain campaign says Obama played race card; calls move 'divisive and wrong' ... Poll: Obama leads McCain in Pennsylvania; McCain tied with Obama in Ohio, Florida ... Ron Paul's followers vow to fight on in West, playing possible spoiler for John McCain ... Effort to get Obama to pick Clinton as his No. 2 ends with conclusion she won't be picked