Anyone who says it doesn’t matter whether Donald Trump or Hillary Clinton wins this election needs their head examined. The damage that Trump could do to our nation with his blend of intellectual laziness, towering policy ignorance and reckless impulsiveness is in a league of its own. Hillary has some real personal ethics issues she needs to confront, but she’s got the chops to be president.

What interests me most right now, though, is a different question. It’s not, “Who are they — our politicians?” It’s, “Who are we — the voters?”

To be specific: Are we all just Shiites and Sunnis now?

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.

And it gives you the sorry spectacle of Clinton surrogates turning themselves into pretzels to defend her, even though it’s obvious that she embraced a pattern of major donors to the Clinton Foundation being given preferential access to her as secretary of state.

Shiites stick with Shiites. Sunnis stick with Sunnis. It’s rule or die, baby. Nothing else matters.

That is not always true in other walks of life. We just got that lesson at the Olympics. American runner Abbey D’Agostino clipped New Zealand’s Nikki Hamblin from behind in the women’s 5000-meter qualifying heat, sending both tumbling to the ground well short of the finish.

The Associated Press reported: “D’Agostino got up, but Hamblin was just lying there. She appeared to be crying. Instead of running in pursuit of the others, D’Agostino crouched down and put her hand on the New Zealander’s shoulder, then under her arms to help her up, and softly urged her not to quit.” They embraced at the finish.

Contrast that with the Egyptian Olympic judoka who, under pressure from his society, refused to shake hands with his Israeli opponent. And how’s Egypt doing these days? Drifting aimlessly.

Yes, I know, politics ain’t bean bag. It’s about winning. But it’s also about winning with a mandate to govern. And right now, everything suggests that the next four years will be just like the last eight: a gridlocked, toxic, Sunni-Shiite, Democrat-Republican civil war, with little search for common ground. That’s how you ruin, not run, a great country.

How will we improve Obamacare? How will we invest in infrastructure? How will we recreate the compromise on immigration that a few brave Republican and Democratic legislators tried in 2013? How will we get corporate tax reform, a carbon tax and some fiscal policy that we so desperately need to propel the economy and control the deficit?

There is no doubt that Republicans during the Obama presidency pioneered and perfected this scorched-earth politics and have now paid a price for it. They let themselves be led around by a group of no-compromise talk-radio gasbags, think-tank ideologues in the pay of one industry or another, Fox News know-nothings and an alt-right fringe, who, together, so poisoned the G.O.P. garden that an invasive species, Donald Trump, just took it over.

That is all the more reason for Clinton to reach out, at the right time, and see if any of them have learned their lesson. There is no way she’ll get anything big done otherwise. We have to break this fever.

It will be a tragedy if center-right Republicans conclude that their only problem is Donald Trump, and that once he’s gone the G.O.P. will be theirs again. Their party is over. They either have to become conservative Democrats or redefine a responsible center-right G.O.P. — with a different base. But it will be equally sad if Clinton wastes the opportunity of a potentially substantial victory, achieved with some Republican votes, to rebuild the political center in this country.

As Americans, we were once summoned by our politics to be participants in a race to the moon. Lately we’ve been summoned by our politics to be spectators in a race to the bottom. We can do better, and we must.