I think we're forgetting that Hilary has huge and permanent negative poll numbers, something above 30 percent, and, for a big chunk of 2007 and 2008, those numbers were either more than or very close than the number of people who merely had a favorable opinion of her.
I can't quite remember the term used, it's something along the lines of a "negative Q rating", but it refers to people who will not vote for her no matter who her opponent is. Run the gay, meth-addicted, lifelong welfare recipient, Muslim, love child of Stalin & Hitler against her and these folks would still vote for Adolph-Ioseb "Sugar Tushie" bin Laden rather than her.
During the 2008 election cycle, the Dems were very concerned about this negative Q rating as it meant that only 70 percent or so of the vote would supposedly be in play. Clinton would be handing any opponent in the general election a huge, almost insurmountable, lead and this led many Democrats to throw their support to Obama once he began to be seen as a plausible alternative.