Hillary Clinton may have endorsed Barack Obama, but winning over her supporters may prove more difficult for Obama than many people thought. A new CNN survey [1] shows that the number of Clinton supporters who plan to vote for Obama has actually decreased since early June from 60% to 54%.

Furthermore, 43% of Democrats now say they’d prefer Clinton to lead the ticket, up from 35% at the beginning of June.

So why are Obama’s attempts to woo Clinton...