WASHINGTON — America’s black voters turned out at a higher rate than other minority groups in 2012 and by most measures surpassed white turnout for the first time, reflecting a deeply polarized election in which blacks strongly supported Barack Obama while many whites just 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 done for the Associated Press.
Census data and exit polling show that whites and blacks will remain the two largest racial groups of eligible voters for the next decade. Last year’s heavy black turnout came despite concerns about the effect of new voter-identification laws on minority voting, outweighed by the desire to reelect the first black president.
William H. Frey, a demographer at the Brookings Institution, analyzed the 2012 elections using census data on eligible voters and turnout, along with November’s exit polling.
He estimated total votes for Obama and Romney in a scenario where 2012 turnout rates for all racial groups matched those in 2004. Overall, 2012 voter turnout was about 58 percent, down from 62 percent in 2008 and 60 percent in 2004.
The analysis also used population projections to estimate the shares of eligible voters by race group through 2030.
The numbers are supplemented with material from the Pew Research Center and George Mason University associate professor Michael McDonald, a leader in the field of voter turnout who separately reviewed aggregate turnout levels across states, as well as AP interviews with the Census Bureau. The bureau is set to release voter turnout data in May.
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 the passage of the Voting Rights Act in 1965.
But the numbers also offer a cautionary note to both Democrats and Republicans after Obama won in November with a historically low percentage of white supporters. With Hispanics now the biggest driver of US population growth, they still trail whites and blacks in turnout and electoral share, because many of the nation’s Hispanics are children or are not citizens.
In recent weeks, Republican leaders have urged a ‘‘year-round effort’’ to engage black and other minority voters.
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 US economy helped overcome doubts and spur record levels of minority voters.
‘‘It remains to be seen how successful Democrats are if you don’t have Barack Obama at the top of the ticket,’’ said Whit Ayres, a GOP consultant advising Senator Marco Rubio, a Florida Republican and possible 2016 presidential contender.