"First, there is the question of how much emphasis Republicans will choose to place on gay marriage, which could motivate their base but increasingly divide Republican voters and independent ones. Next, how much might Mr. Obama’s stance be embraced or opposed by African-Americans, who have more conservative attitudes about same-sex marriage than other Democrats? Finally, could the issue motivate younger liberals and Democrats, who tend to support same-sex marriage, to turn out for Mr. Obama when they might not otherwise?"