On the morning of June 26, 2015, barely two hours after the Supreme Court handed down its decision to uphold same-sex marriage, Barack Obama delivered the eulogy for nine murder victims at the Emanuel African Methodist Episcopal Church in Charleston, South Carolina. With impeccable timing, he moved from word to song, invoking grace and then singing of its sweetness and redemptive power. To some practiced ears, the president resembled an earnest college boy trying to mimic a field recording. But whether his performance was improvised or not, the product of spirit feel or political instinct, it was a rhetorical coup,…