More and more of our politics resembles the core sectarian conflict in the Middle East between these two branches of Islam, and that is not good. Because whether you’re talking about Shiites and Sunnis — or Iranians and Saudis, Israelis and Palestinians, Turks and Kurds — a simple binary rule dominates their politics: “I am strong, why should I compromise? I am weak, how can I compromise?”

With rare exceptions, the politics of the Middle East is just a seesaw game between those two modes of zero-sum, rule-or-die thinking. Rarely, these days, does either party stop to seek or forge common ground. It’s just: I am strong, so I don’t have to meet you in the middle, or I am weak, so I can’t meet you in the middle. You can see how well it’s worked for them.

Politico last week reported that while some G.O.P. officials may vote for Hillary, they are already sketching plans “to stymie a President Hillary Clinton agenda.” Liberals are already warning Clinton not to bring Republicans into her cabinet or explore meeting them halfway. Have a nice day.

That kind of sectarian/tribal thinking, now reinforced by left-right social media enforcers, gerrymandering and giant campaign funders, gives you the sorry spectacle of House Speaker Paul Ryan saying, without embarrassment, that Trump’s pronouncements are a “textbook” example of racism, but he’s supporting Trump anyway.