A quarter-century after the post-Cold War zenith of liberal democracies and neoliberal economics, illiberalism and authoritarianism are on the march. It’s open season for anyone’s inner bigot. Violence is in the air, awaiting a spark. The winning political card today, as Mr. Trump has shown and Marine Le Pen may demonstrate in the French presidential election next year, is to lead “the people” against a “rigged system,” Muslim migration and the tyrannical consensus of overpaid experts. The postwar order — its military alliances, trade pacts, political integration and legal framework — feels flimsy, and the nature of the American power undergirding it all is suddenly unclear. Nobody excites Mr. Trump as much as Russia’s Vladimir V. Putin, who is to democracy what a sledgehammer is to a Ming vase. Strongmen and autocrats everywhere — not least in Egypt and the Gulf states — are exulting at Mr. Trump’s victory.

It is too early to say what Mr. Trump will do and how many of his wild campaign promises he will keep, but it’s safe to predict turbulence. Irascibility, impetuosity and inattention define him, however curtailed they may prove to be by his entourage and the responsibilities of power. He is, for now, in over his head.

NATO will grow weaker. Baltic States will feel more vulnerable. Syria’s Bashar al-Assad, backed by a Putin-Trump entente, will grow stronger. Chinese-American trade tensions will sharpen, in approximate sync with military tensions in the East and South China seas. The Iran nuclear deal, painstakingly negotiated by the major powers, could unravel, making the Middle East exponentially more dangerous. Any jihadi attack or other assault on America will not be met with restraint; Mr. Trump seems to regard nukes as an underused asset.

Fossil fuels will make a comeback. The world’s Paris-enshrined commitment to fight climate change will be undermined. The approximately 65 million migrants on the move, about one-third of them refugees, will find shelter and dignity scarce as xenophobic nationalism moves into the political mainstream across Central Europe and elsewhere. Technology’s implacable advance, and the great strides being made by artificial intelligence, will test Mr. Trump’s promise to bring manufacturing jobs back to America. Some forms of employment are gone forever, and not even a self-styled savior can conjure their return. The Trans-Pacific Partnership already looks dead; other trade deals, including the North American Free Trade Agreement, which symbolized the ever-more-open trading system of past decades, could be nixed or substantially diluted.

Will all this assuage the people’s ire? Perhaps Mr. Trump really does have some fairy dust he can scatter for a while. But of course “the people” were only part of a divided population, millions and millions of whom did not want — and will resist — the global nationalist and authoritarian lurch. They will do so on the streets, in the courts, via the press and through the checks and balances the framers of the Constitution created precisely to rein in a demagogue. Still, Mr. Trump has enormous powers, a Republican-controlled Congress and a mission to make America great again, whatever that means or takes.