Sean Trende’s low white turnout assertion wrecks the Left’s Minority Triumphalism  and so it is to be expected that their apparatchiks are deploying to contest it, as Steve Sailer has noted .
But the article Steve links to There Aren't As Many Missing Voters As It Seems  Nate Cohn The New Republic November 8, 2012 concludes with a devastating concession:
Given the initial exit poll data and the current national popular vote tally, it looks like white turnout might have declined slightly since 2008. I'm holding off judging just how much until the final exit polls and results are reported...
John McCain lost in 2008 because of low white turnout . Romney and Karl Rove failed to reverse that.
Romney lost the presidency. Karl Rove got rich.