Based on my observations and discussions with people I know, if Clinton wins the nomination, most people I know will vote for McCain.   And I live in San Francisco, perhaps the most liberal place in the US, and most of my friends are very liberal.  

Obama, however, is a different story.  Even staunch republicans I know like him and might vote for him.

My conclusion is that Clinton makes a McCain victory likely, whereas Obama is a wildcard.

Personally, I think the country needs Obama.   Clinton brings nothing new to the table other than gender, but Obama is really something different.   The country needs uniting and it needs a better international image, both of which, I think, can be achieved by Obama.