The Obama phenomenon is hurtling past the best analogies that we have for it. Three years ago Barack Obama shot onto the national political scene with a sensational speech at the Democratic National Convention. Two years ago he joined the U.S. Senate as its only African-American member. A year ago he was still admonishing admirers to give him time to accomplish something before talking up an Obama presidency. Today he is running for president because he has generated too much excitement to wait for another political season.