By Nedra Pickler DES MOINES, Iowa -- Even before Oprah Winfrey had left the building during the weekend's big campaign rallies for Barack Obama, the candidate's team had begun an intensive follow-up effort -- trying to turn tens of thousands of Oprah fans into Obama voters.

Barack Obama's hopes for the Democratic nomination hinge on getting hundreds of thousands of new voters fired up enough to actually turn out - and on spending a good chunk of his $80 million at the very end of a front-loaded campaign.