For decades, and especially during the past seven years, political media have complained about what they say is a lurch toward right-wing extremism by the Republican Party. The rise of the Tea Party, congressional GOP resistance to President Obama’s agenda, opposition to gay marriage, the lack of abortion supporters in the party— all of it has been depicted as evidence of extremism and being out of touch with the public.

This superficial and self-serving analysis ignored the existence of the reciprocal phenomenon — the Democratic Party’s lurch to the left.