The timing of President Barack Obama's statement in support of gay marriage was no accident, according to Emory University political scientist Andra Gillespie.

"Obama needs to shore up his support among progressives and young people, and he figured this would be a way to do it," she says.

Public opinion polls now show a slim majority of Americans support gay marriage, yet Obama's announcement is not totally risk-free, says Gillespie. "Yes, most people opposed to gay marriage were already not voting for him, but this announcement could galvanize that constituency, who is still not enthused with Mitt Romney."

When it comes to African American voters, most still will not vote Republican, says Gillespie, but "there is a chance that the most religious black Democrats may see their enthusiasm dampened by this announcement." In a close election, voter enthusiasm matters, she adds, "but the president is probably confident that gay marriage is not the most salient issue for black voters."

Gillespie, associate professor of political science, is the author of the new book "The New Black Politician: Cory Booker, Newark and Post-Racial America."