Rasmussen Reports, which had Mitt Romney leading President Obama on the final day of the presidential campaign and picked the winner in just three of nine swing states, explains:
“A preliminary review indicates that one reason for this is that we
underestimated the minority share of the electorate. In 2008, 26% of
voters were non-white. We expected that to remain relatively constant.
However, in 2012, 28% of voters were non-white. That was exactly the
share projected by the Obama campaign. It is not clear at the moment
whether minority turnout increased nationally, white turnout decreased,
or if it was a combination of both. The increase in minority turnout has
a significant impact on the final projections since Romney won nearly
60% of white votes while Obama won an even larger share of the minority
vote.”
“Another factor may be related to the generation gap. It is interesting
to note that the share of seniors who showed up to vote was down
slightly from 2008 while the number of young voters was up slightly.”