“Americans’ deep bias against the political party they oppose is so strong that it acts as a kind of partisan prism for facts.” It “now operates more like racism than mere political disagreement,…” The deepening antipathy to the opposition party seems to have begun in the 1980s.
That is, disputes over policy issues now seem to entail a positive or negative judgment of the person making the argument. One researcher suggests that “we [now] hold party identity as something akin to gender, ethnicity, or race—the core traits that we use to describe ourselves to others.” Just as exogamous marriage (across racial or social class divides) is much less common than endogamous marriage, politically exogamous marriage is rare. One survey found only 9 percent of marriages were between a Republican and a Democrat.
Apparently, neither Republican nor Democratic voters adopt a critical stance when evaluating information. Instead, they tend to rely on the endorsement of that information by someone or some organization that they already trust. Given the increasingly cloistered political communities in which they dwell, the people to whom others look for endorsement tend to be people with essentially the same beliefs. Deeply partisanized voters seek out or respond to negative stories about the opposition party and politicians. The endless liking/sharing of political posts on Facebook publically affirms membership in the group. There is a greater danger than thrown drinks or thrown punches among individuals. Politicians have already cleared out the middle ground in most legislatures. What if they are driven to adopt ever-more extreme positions to keep up with their bases?
Something similar happened in Europe between the two World Wars. Pre-First World War politics had pitted conservatives against liberals, with rapidly growing socialist parties marginalized to the extreme left. The war changed all this in many places. Wartime grievances among workers at first enlarged the socialist parties. However, the Russian Revolution created the Communists as an entirely new and more radical party on the left. At about the same time, a radical new party emerged on Europe’s right, the Italian Fascists. Early in the Thirties, the Great Depression sent voters in many places streaming toward other parties of the radical right, like the Nazi Party in Germany and the various “ligues” in France. The effect of the radical movements on the extremes came in the democratic Socialists having to talk more like the Communists and the conservatives having to talk more like the fascists. The middle ground in politics, where compromise traditionally had taken place, began to clear out. Democratic systems on the Continent became paralyzed as the need for action became dire.
Then came running and screaming.
 Amanda Taub, “Partisanship Is the Real Story Behind Fake News,” NYT, 12 January 2017.
 That would trace the roots to the period of the Reagan Administration, followed—eventually—by the Clinton Administration.
 This may include supposedly dispassionate researchers investigating the phenomenon. One quoted in Amanda Taub’s story says “If I’m a rabid Trump voter and I don’t know much about public affairs,…”
 Can Republican and Democratic bathrooms be far behind?
 Thus, many Republicans would lap up news from Fox, while many Democrats would look to MoveOn.org for all their meme needs.
 We’ve got the “Australian ballot.” Maybe we could use the “Australian opinion”?
 This link shows one example. https://www.youtube.com/watch?v=n8HGTmANHyU However, two cousins (Democrats) returning from the Midwest just after the Republican convention said that they felt threatened by the pro-Trump people on the plane.
 In the case of Britain, the Labour Party soon eclipsed the Liberal Party.