When the Berlin Wall came down, a wall went up in Washington. Democrats and Republicans, who had co-operated as a matter of routine during the cold war, grew distant from around 1989. Perhaps the disappearance of a common adversary called the USSR freed the two parties to turn on each other.
Is this too neat? Something a psychotherapist might say? Well, consider a few data points.
Before 1989, there had been one presidential impeachment in US history, or two if we count the one Richard Nixon pre-empted by quitting. There have been three in the short time since. Before 1989, the Senate would often approve a judge for the Supreme Court without a single dissenting vote. This hasn’t happened once since. Before 1989, landslide presidential victories were frequent. No one has commanded broad enough support to reach even 400 electoral college votes since George HW Bush, the last cold war president. I suppose it could all be a coincidence. But other partisan forces that emerged after the wall fell include Fox News (1996), its liberal antagonist MSNBC (1996) and Newt Gingrich’s “revolution” in Congress (1994).