Looking at these percentages from another perspective, only 13 percent of all non-voters in 2004 were African-Americans. Even if non-voting blacks came out this election in numbers twice that of every other group of non-voters, it would not turn the election upside-down. There is a ceiling effect on how influential a surge in black turnout can be because of African-Americans’ comparatively small share of non-voters.

The development that would make black turnout more significant would be a surge in registration of African-Americans. This is a realm where the black population still lags in a meaningful way. According to the Census survey, only 69 percent of African-Americans are registered. While this compares very favorably to registration rates of other ethnic and racial minorities (52 percent of Asians and 58 percent of Hispanics are registered, according to the Census Bureau), it significantly trails the 75 percent rate of registration among non-Hispanic whites. Because of non-registration, the electoral participation of all black adults is 60 percent, trailing whites by seven percentage points. If blacks closed that gap completely, it would bring 1.7 million additional African-American voters to the polls this fall.