As Americans have more experience with Bush their opinion of him drops.
Which is reflected also in rise in US popular view around the world now that Bush is leaving.
Experience of the voters + Diversity of the voter = More predictive expectation.
In 2003 the high view Americans had of Bush was from 1 a short period of his term and was opposed to the global view on Bush at that time. Today Americans have 5 more years of experience of Bush and their low regard for him not only matches the global opinion of him but also more closely represents the general failure historians and political scientists see Bush to be.
Diversity + Experience makes the wisdom of crowds in to the wisdom of experts.