That isn’t to say that partisan polarization doesn’t have some bad effects, but at this point it’s a reality that we can’t just wish away. It has multiple causes, but the most important one is that the parties have become much more ideologically coherent today than they were, say, 50 years ago. Back then the Democratic Party in particular was an uneasy coalition of northern liberals and southern conservatives, whose bond to the party was forged in the Civil War. But once Democrats embraced the cause of civil rights in the 1960s and Lyndon Johnson signed the Civil Rights Act and the Voting Rights Act, that bond was severed. It took a few decades to shake out completely, but eventually all the southern conservatives (including segregationists and racists in the mold of Strom Thurmond and Jesse Helms) left the Ds for the Rs.

As they did, liberal Republicans increasingly felt alienated from their party, and so many of them crossed over to the Democrats. Fast forward to today, and you have virtually no more liberal Republicans or conservative Democrats, especially among officeholders who have to win primary campaigns in order to represent their parties. Even if there are times when they agree on a particular issue (sometimes for better, sometimes for worse), on the the whole you have two parties that are completely distinct.