Politico highlights an Associated Press analysis:

America’s blacks voted at a higher rate than other minority groups in 2012 and by most measures surpassed the white turnout for the first time, reflecting a deeply polarized presidential election in which blacks strongly supported Barack Obama while many whites stayed home.  Had people voted last November at the same rates they did in 2004, when black turnout was below its current historic levels, Republican Mitt Romney would have won narrowly, according to an analysis conducted for The Associated Press.

…Overall, the findings represent a tipping point for blacks, who for much of America’s history were disenfranchised and then effectively barred from voting until passage of the Voting Rights Act in 1965.

…The 2012 data suggest Romney was a particularly weak GOP candidate, unable to motivate white voters let alone attract significant black or Latino support. Obama’s personal appeal and the slowly improving economy helped overcome doubts and spur record levels of minority voters in a way that may not be easily replicated for Democrats soon.

Romney would have erased Obama’s nearly 5 million-vote victory margin and narrowly won the popular vote if voters had turned out as they did in 2004, according to Frey’s analysis. Then, white turnout was slightly higher and black voting lower.