(Drew Angerer/Getty Images)
Opinion writer

Tribalism is one of those things that everyone laments yet everyone engages in, to one degree or another. It’s hard not to see political developments through the filter of whether they’re good for people like you, defined by your race, your religion, your gender, your home state, your political party or any of a hundred other ways.

But in our lifetimes, there has never been a president more explicitly tribal than Donald Trump. As we’re seeing right now on our southern border, that tribalism emerges not just in rhetoric but also in brutal policy decisions. And he has five justices on the Supreme Court who seem determined to set that same perspective down in binding legal precedent.

The trouble is that in the United States, we have a document known as the Constitution that mandates equal treatment even for people you don’t like. So today, the Supreme Court handed down a decision upholding Trump’s travel ban, in the process insisting that it had nothing to do with what Trump said over and over again it was designed to do.

This all began during Trump’s 2016 presidential campaign, which he built on a foundation of xenophobia, fear and hatred of “the other.” Among other things, Trump proclaimed that he wanted “a total and complete shutdown of Muslims entering the United States.” Told that such a nakedly discriminatory policy was obviously unconstitutional, he instructed his aides to devise a kind of Muslim Ban Lite, one that might have some chance of being upheld by a friendly Supreme Court. After a few iterations, they arrived at the one the court ruled on today, which bars entry from a group of majority-Muslim countries, plus North Korea and Venezuela thrown in.

In its decision, the court’s conservative majority notes that the presidential order establishing the travel ban “says nothing about religion.” They also note that most of the world’s Muslims are unaffected by the ban, which is true. What they don’t say, however, is that the ban has almost nothing to do with any genuine worries about security; as the court’s liberals said in their dissent, the ruling “leaves undisturbed a policy first advertised openly and unequivocally as a ‘total and complete shutdown of Muslims entering the United States’ because the policy now masquerades behind a façade of national-security concerns.”

In the recent Masterpiece Cakeshop case, the conservatives found proof in the comments of a member of a state civil rights commission that the real purpose of a ruling against a baker who wanted to discriminate against a gay couple was anti-religious animus. But in this case they decided that Trump’s repeated statements that the purpose of this ban was to discriminate against Muslims should simply be ignored.

For the president, the fact that this ban discriminates only against some Muslims and not all Muslims isn’t that much of a problem. The ban is almost entirely symbolic — not if you’re a Libyan student hoping to study in the United States or a Syrian American wanting to see her parents before they die, but for Trump. It’s a way of telling the world that we don’t like Muslims and we don’t want them here. It wasn’t the ban he preferred, but it was the ban he and his people thought they could get upheld in the Supreme Court. And they were right.

Trump’s tribalism consists of many concentric circles, each with borders that must be reinforced, sometimes literally (build that wall!) and sometimes symbolically. When he deals with the rest of the world, he emphatically rejects the idea that we could have any common interests or goals with other countries, because there is America and then there is everyone else, the foreigners who are trying to take advantage of us or undermine us.

International relations, in the Trump view, is a zero-sum contest of all against all, and if we aren’t besting and humiliating others then we’re the losers, the suckers, the chumps. Any agreement where all sides believe they’ve gotten something worthwhile must be a terrible deal in which we got scammed, which is why Trump walked away from the Paris climate accord, the Iran nuclear deal and the Trans-Pacific Partnership.

Here at home, Trump says that we need to be on guard against foreign infiltration because those wanting to come here (unless they’re from a country such as Norway where almost everyone’s white) are nothing but a collection of criminals, terrorists and assorted lowlifes who want to kill your family, or at the very least destroy all that’s good about America. They are, quite literally, not human; Trump describes immigrants as an infestation. That, too, is one of the hallmarks of tribalism: the belief that those in another tribe are less than human, and it’s therefore morally permissible to do all manner of horrible things to them. Like tearing their children from their parents’ arms. So it should not be a surprise that Trump’s party has moved from its previous position that it only opposes illegal immigration but supports legal immigration toward seeking new laws to drastically restrict legal immigration as well.

It goes even farther. While plenty of his predecessors may have looked more kindly on their supporters than on those who rejected them, Trump alone doesn’t even bother to pretend that he wants to be a president for all Americans. After the election, he went on a “thank you tour,” visiting only states that he won, a little extra way of telling the rest of the country to buzz off. At rallies, Trump regularly tells his most passionate supporters that they’re better human beings than other Americans. “You’re smarter, you’re better, you’re more loyal. We have the greatest base in the history of politics,” he said yesterday in South Carolina.

We’ve heard similar things from other politicians, who extol “the heartland” or small towns — in other words, places where lots of Republicans live — as the wellspring of virtue, the “real America” where all that is righteous and good may be found. But few have been so explicit as Trump, to say that supporting him makes you a superior person.

That is the innermost of those concentric circles of tribalism: Trump himself. The ultimate measure of whether you’re allowed to remain a part of Us or are banished to the realm of Them is whether you support, praise and serve Trump. For all the bigotries and prejudices he promotes and seeks to enshrine in law and policy, nothing matters to him more than that.