He’s got the Oprah machine behind him.
Nobody knows how tough that support will hang, though. Oprah's audience is mostly female, mostly uninterested in politics, and is basically supporting Obama because Oprah says they should. If the Clintons manage to hang something on Barack that can't easily be shaken off, I just don't see that crowd crawling over broken glass to go to the polls. If Oprah was actually the candidate, well, different story.
Oprah may well end up regretting that she got involved in this race.