Americans are voting early in record numbers before the November 8 presidential election.
Less than one week before Election Day, more than 29 million people have cast early ballots, nearly twice as many as those who voted early during the same period four years ago, according to the United States Elections Project.
Despite heavy turnout among early voters, ballots cast so far by African-Americans have not matched 2012 levels, fueling concern among Democratic candidates such as Hillary Clinton who have historically received the broad support of this segment of the electorate.
Lower levels of early voting among African-Americans has prompted a warning from President Barack Obama, America's first black president. In a pre-taped radio interview that was broadcast Wednesday, Obama said on the "Tom Joyner Morning Show" that if his legacy is to be protected, African-American voters must vote in order to "pass the baton" to a like-minded successor.
IN PHOTOS: Early Voting in Full Swing across U.S.
Heavy early voting among the overall U.S. population could be due to a variety of factors, according to the Early Voting Information Center at Reed College in the northwestern city of Portland, Oregon.
The convenience of early voting, the intensity of the campaign, sharp contrasts between the presidential candidates and more focus on early voting mobilization may be contributing factors, the Early Voting Information Center's Paul Gronke wrote in a commentary.
"What is clear, however, is that early voting could be a key indicator of who is winning the horse race," Gronke added.
As Clinton and Republican presidential candidate Donald Trump enter the final stretch, their campaigns are concentrating on key battleground states.
Obama campaigned Wednesday in North Carolina, where a federal appeals court blamed Republicans for an "almost surgical" attack on black voter turnout by approving several voter suppression measures, including a curtailment of early voting opportunities.
Early black voter turnout in North Carolina, where Clinton still enjoys a slight edge, has dropped 16 percent from 2012 levels, while white turnout has climbed 15 percent.
While turnout is lower among black voters, Democrats are hoping to offset it by winning significant support from two other key constituent groups: Latinos and college-educated women.
The Trump campaign is spending much of its energy on the must-win battleground state of Florida, where more than 44 percent of early ballots have been cast compared to 2012 levels, according to the Early Voting Information Center.
The center reports that the highest rate of early voter turnout has been in Louisiana, where early voting already has exceeded the total number of early ballots cast in 2012. Florida, Georgia and Tennessee also are showing very high turnout, with levels reaching at least 80 percent of the 2012 totals.
Of the 11 battleground states identified by Politico, the Early Voting Information Center reports that only New Hampshire and Pennsylvania have not experienced early voter turnout that exceeded more than half of the 2012 levels.