Those who study electoral reform tend to agree on one of two things. Voting-system change is either a defensive move by parties that expect to be swallowed. Or it is a power-grab, tempered by the need to bargain with other parties. So it has been in countries with more than two parties.
In the United States, where we have only two parties, the turn has not been to party-based forms of proportional voting (PR). Party faction is the unit of analysis. The question for a faction is: do we control nominations? This is why PR in America has been the single transferable vote (STV) — with nomination by petition to boot. Going back to the power-grab model, the need to bargain with a dominated faction in the other party is key. The price it demands is open endorsement, otherwise known as an end to “boss rule.”
Two things strike me about modern-day politics. One is new interest in STV systems, especially after 2016. The second is uncertainty within each party about which of its factions is dominant. We may not know until 2020, but the current buzz speaks for itself.
So, with these points in mind, I made a few memes.
Here is one for Republicans.
And here is one for the Democrats.