Progressives and conservatives traditionally have exhibited different attitudes to the lessons of history. While conservatives have tended to take cues from the past as they build measured hopes for the future, progressives have urged that we break free from tradition in order to create bold and ambitious blueprints for a society they consider to be more just. In the United States, however, this pattern appears to be breaking down, as it is now progressives who tend to embrace a more rigid, backward-looking approach, especially on issues tied to identity. Unlike conservatives, progressives aren’t looking to revive a better, sometimes idealized version of their country. But they have become bogged down in the politics of historical redress, at the expense of forward-looking policies that would actually improve people’s lives. A microcosm of this larger tendency was put on display during last month’s Democratic primary debates, which touched on the issue of urban gun violence. No Democratic presidential candidate expressed a sense of responsibility for the plague of violent crime in America’s cities, even though the largest …