Normally, when your main geopolitical rivals are shooting themselves in both feet, the military manual says step back and enjoy the show. But I take little comfort in watching China burning money and Russia burning food, because in today’s interdependent world we’re all affected.

I also find no joy in it because we Americans, too, have started burning our most important source of competitive advantage — our pluralism. One of our two political parties has gone nuts and started following a pied piper of intolerance, named Donald Trump.

First, we watched China’s leadership burn money — trying to prop up a ridiculously overvalued stock market by buying falling stocks with government savings, and then seeing that market continue to collapse because the very fact that the government was intervening suggested no one knew what these stocks were worth.

The Wall Street Journal reported on July 30 that the “state-owned China Securities Finance Corporation has been spending up to 180 billion yuan a day ($29 billion) to try to stabilize stocks.” Since the Shanghai exchange has fallen sharply since then, the amount of money China burned trying to prop up already unrealistic valuations must be staggering.

The economic management team in Beijing has seriously lost its way. But leaders do funky things when the ruling party’s bargain with its people is “we get to rule and you get to get rich.” Collapsing markets can quickly lead to collapsing legitimacy.

Ask the Russian president, Vladimir Putin. He burned the eastern quarter of Ukraine to distract the Russian middle class from his economic mismanagement and illegitimacy.

Putin decided that building his own Silicon Valley — the Skolkovo Innovation Center outside of Moscow — was too hard. So to build his legitimacy he chose nationalism and seized Crimea instead. Putin prefers to manufacture chips on his shoulder than microchips. When the Crimea annexation nationalist sugar high wore off, Putin started burning food imported from countries sanctioning Russia for seizing Crimea from Ukraine.

As The Times reported on Aug. 6, “Following an order by President Vladimir V. Putin, officials threw huge piles of pork, tomatoes, peaches and cheese into landfills and garbage incinerators. The frenzy, remarkable even by the standards of Russia’s recent politicization of food supplies, was gleefully reported by Russian state television.” This is in a country where food prices have soared because of the collapse of the ruble.

My fear is that once Putin’s food-burning nationalist sugar high wears off, he’ll burn up another neighbor. Estonia, please beware.

Alas, though, America has joined this assets bonfire. We’re now in a world where all top-down authority structures are being challenged. It’s most obvious in the Arab world where you have pluralistic countries that lack pluralism and so could be held together from the top-down only by an iron fist — and when that iron fist got removed they spun apart. America’s greatest advantage is its pluralism: It can govern itself horizontally by its people of all colors and creeds forging social contracts to live together as equal citizens.

It not only makes us more stable but also more innovative, because we can collaborate internally and externally with anyone anywhere, leveraging more brainpower. Who is the new C.E.O. of Google? Sundar Pichai. Who is the new C.E.O. of Microsoft? Satya Nadella. Mark Zuckerberg’s family did not come over on the Mayflower.

But right now we’re messing around with that incredible asset. Yes, we must control our borders; it is the essence of sovereignty. It has been a failure of both our political parties that the Mexican-American border has been so porous. So I am for a high wall, but with a very big gate — one that legally lets in energetic low-skilled workers and the high-I.Q. risk-takers who have made our economy the envy of the world — and for legislation that provides a pathway for the millions of illegal immigrants already here to gain legal status and eventually citizenship.

In June 2013, the Senate, including 14 Republicans, passed a bill that would do all that. But the extremists in the G.O.P. House refused to follow, so the bill stalled.

And now we have Trump shamelessly exploiting this issue even more. He’s calling for an end to the 14th Amendment’s birthright principle, which guarantees citizenship to anyone born here, and also for a government program to round up all 11 million illegal immigrants and send them home — an utterly lunatic idea that Trump dismisses as a mere “management” problem. Like lemmings, many of the other G.O.P. presidential hopefuls just followed Trump over that cliff.

This is not funny anymore. This is not entertaining. Donald Trump is not cute. His ugly nativism shamefully plays on people’s fears and ignorance. It ignores bipartisan solutions already on the table, undermines the civic ideals that make our melting pot work in ways no European or Asian country can match (try to become a Japanese) and tampers with the very secret of our sauce — pluralism, that out of many we make one.

Every era spews up a Joe McCarthy type who tries to thrive by dividing and frightening us, and today his name is Donald Trump.