Ehrman, a former evangelical who nows considers himself (at best) an agnostic, decided to take up this question, and that is the subject of his new book, "Did Jesus Exist?: The Historical Argument for Jesus of Nazareth." Ehrman's conclusion is that, yes, Jesus did exist, and he marshals historical evidence on behalf of this conclusion. Ehrman was recently interviewed on National Public Radio about his new book, and the audio recording and transcript of the interview can be found here: "'Did Jesus Exist?' A Historian Makes His Case." It's interesting and worth your time if you're interested in the subject.