Among liberals, it’s almost universally assumed that of the two major parties, it’s the Republicans who have become more extreme over the years. That’s a self-flattering but false narrative.
This is not to say the Republican Party hasn’t become a more conservative party. It has. But in the last two decades the Democratic Party has moved substantially further to the left than the Republican Party has shifted to the right. On most major issues the Republican Party hasn’t moved very much from where it was during the Gingrich era in the mid-1990s.
To see just how far the Democratic Party has moved to the left, compare Barack Obama with Bill Clinton. In 1992, Mr. Clinton ran as a centrist New Democrat. In several respects he governed as one as well. He endorsed a sentencing policy of “three strikes and you’re out,” and he proposed adding 100,000 police officers to the streets.