President Obama will mark the 50th anniversary of the March on Washington Wednesday against the backdrop of an electorate that is sharply divided along racial lines. The gap between white and black voters in 2012 was wider for Obama than it had been for any Democratic nominee in nearly three decades.

Ninety-three percent of black voters supported President Obama in 2012, exit poll data show. By comparison, just 39 percent of white voters supported a second term for the president. The 54-point racial gap (nearly identical to the 52-point gap in Obama's first election in 2008) was the widest since 1984, when blacks were 55 points more likely than whites to back Democratic nominee Walter Mondale.

Throughout history, the gap between black and white voters has fluctuated. Between 1988 and 2004, it was consistently between 41 and 48 points for the Democratic nominee. In the 1950s into 1960, Gallup polling showed a much smaller divide. The gap was as narrow as 19 points in 1960.

The daylight nearly doubled to 35 points in 1964, when Lyndon Johnson defeated Barry Goldwater by a very wide margin. That election came about a year after Martin Luther King, Jr. gave his "I Have A Dream" speech at the March on Washington.

Obama's 2012 victory was due in no small part to both strong support and strong turnout from minority voters. No other Democratic president in history had won with as large a deficit among white voters.

Blacks made history in 2012, voting at a higher rate than whites for the first time ever, Census Bureau data show. Sixty-six percent of eligible black voters cast ballots, compared to 64 percent of eligible white voters.

The question moving toward 2016 is how and if turnout and the racial gap will shift without Obama, the nation's first African American president, on the ballot.