American public opinion tends to be sticky. Although the news cycle might temporarily affect the public's mood on contentious issues like abortion, the death penalty, or gun control, public opinion toward these issues has remained remarkably constant over decades. There are notable exceptions, however, particularly with regard to divisive issues that highlight identity politics. For example, over the past three decades, public support for same-sex marriage has risen from scarcely more than a tenth to a majority of the population. Why have people's minds changed so dramatically on this issue,...