A paper recently released by two University of Maryland economists, Craig Garthwaite and Tim Moore, tries to quantify Oprah Winfrey's influence over her fans with regards to the Democratic primaries and generating votes. From the paper's abstract:
Candidates in major political contests are commonly endorsed by other politicians, interest groups and celebrities. Prior to the 2008 Democratic Presidential Primary, Barack Obama was endorsed by Oprah Winfrey, a celebrity with a proven track record of influencing her fans’ commercial decisions. In this paper, we use geographic differences in subscriptions to O! – The Oprah Magazine and the sale of books Winfrey recommended as part of Oprah's Book Club to assess whether her endorsement affected the Primary outcomes. We find her endorsement had a positive effect on the votes Obama received, increased the overall voter participation rate, and increased the number of contributions received by Obama. No connection is found between the measures of Oprah's influence and Obama's success in previous elections, nor with underlying local political preferences. Our results suggest that Winfrey’s endorsement was responsible for approximately 1,000,000 additional votes for Obama.
The full paper (with lots of cool equations) can be found HERE.
Disclaimer: the point of this post was to simply address the level of influence certain personalities have over consumers and is not an endorsement of any particular party or candidate 
