The polarization in today’s Congress has roots that go back decades

It’s become commonplace among observers of U.S. politics to decry partisan polarization in Congress. Indeed, a Pew Research Center analysis finds that, on average, Democrats and Republicans are farther apart ideologically today than at any time in the past 50 years.

But the dynamics behind today’s congressional polarization have been long in the making. The analysis of members’ ideological scores finds that the current standoff between Democrats and Republicans is the result of several overlapping trends that have been playing themselves out – and sometimes reinforcing each other – for decades....