From Seth Masket: Parties don't get to choose their own adventure

We've been discussing the shift Democrats made on civil rights in the mid 20th Century and its ongoing consequences. Here's an observation that these shifts don't happen that often:

Huge shifts are the norm? On the contrary -- they're incredibly rare! The Democrats' shift from being the party of white supremacy to the party of civil rights was pretty much a singular act in American political history. Parties rarely pull off a major shift on a hot-button issue (that's what killed the Whigs in the 1850s), and indeed it was a very costly shift for the Democrats, breaking their electoral lock on the southern states and ultimately ending their four-decade run of controlling the House of Representatives. To be sure, parties do evolve slowly on some issues, but the parties are much better defined by consistency than change.