President Trump arrived in Buenos Aires, Argentina, on Thursday night for the annual G-20 summit, which is likely to be something between a waste of time and a disaster.

In part, this stems from the ramshackle nature of the organization—the leaders of 20 nations (or, actually, 19 nations plus the European Union) assembled to discuss a mishmash agenda, with no binding resolutions attached.

But to the extent that things turn disastrous, the problem lies with Trump. Even something as unwieldy as the G-20 can be molded to good ends through shrewd strategy and adroit diplomacy, neither of which Trump possesses in the slightest measure. Quite the contrary: hence the anticipatory shudders no doubt reverberating through the bones of all the other attending leaders and several of Trump’s own aides.

Other, smaller summits of this sort once served a concrete purpose. For instance, the Group of Seven (G-7), which consists of the world’s seven largest economic powers, was created in 1973 to manage global finances after fixed exchange rates fell apart.

Now, though, we live in a “G-Zero” world, as political scientist Ian Bremmer puts it—a world of collapsed power blocs, where no one state (or alliance of states) is able to shape events globally across a wide range of issues. International politics has become a more complex game. Even large nations are rarely able to assert their power; they have to wrangle for dominance or influence with smaller or less-powerful nations that may have special skills or intense interests in a specific region (such as the Middle East or Asia-Pacific) or a specific endeavor (such as trade).

There are few more dangerous people than a powerful idiot who thinks he’s a genius.

In this setting, precisely because of its looseness, the G-20 can be a forum where leaders do this wrangling—probe possibilities, form coalitions, offer deals, make threats. Sometimes this is done in the formal sessions; more often, it’s done at informal “bilaterals,” one-on-one meetings behind closed doors. Engaging in this wrangling requires a few things: some cards to play, a firm awareness of your own interests, and a deep knowledge of the other leaders’ interests.

Trump has cards to play, but he knows nothing about interests—neither his own country’s nor the other countries’, or how those might collide or converge. Worse still, he doesn’t think he needs to know about them. When asked at press conference at Mar-a-Lago last week whether he’s been preparing to meet the leaders, especially Chinese President Xi Jinping, with whom he’s been waging a trade war, Trump replied that he didn’t need to prepare. “I have been preparing for it all my life,” he said. “I know every ingredient, every stat. I know it better than everybody knows it. My gut is always right.”

A few things are worth noting about these remarks. First, in his prior career as a real estate magnate, Trump had some crafty dealings with contractors, tenants, unions, and the New York City Buildings Department, but negotiating with the president of China is something very different. In short, he has not been preparing for this all his life.

Second, it’s not clear just what ingredients and statistics Trump thinks he knows, or needs to know, that give him a leg up at the G-20, but even if there’s something to his claim, it’s irrelevant. Oscar Wilde once defined a cynic as “a man who knows the price of everything and the value of nothing.” That’s Trump, though cynic barely begins to hint at the depths of his shallowness.

Third, anyone who thinks he knows something “better than everybody knows it” is either a genius or an idiot, and there are few more dangerous people than a powerful idiot who thinks he’s a genius.

Finally, anyone who not only trusts his gut but believes it’s “always right” should be disqualified from making judgments that affect the lives of millions. Many talented people, from all walks of life, have well-honed instincts, and yes, some of them feel the rumblings of those instincts in their guts, but their instincts have been formed and sharpened by education and experience. Trump’s gut is just a gut.

Trump makes judgments about one issue or one country at a time, with no assessment of how they affect his positions with other issues or other countries. As a result, in almost all of his dealings, he has alienated every leader who might have been a useful ally in some other context.

For instance, Syria is a complicated conflict; it might be impervious to settlement by anyone. But if there were a diplomatic solution, it would have to involve a consortium of nations—including Russia, Iran, Turkey, and Syria itself—and Trump has either annoyed or sent puzzlingly mixed messages to all of them. Another example: Trump wants to isolate Iran; to do that effectively, he would need the cooperation of its trading partners (actual or potential) in Europe, Russia, and China—and he has angered all of them. He wants to play trade-war games with China; to do that well, he would need to form a common front with Canada and the Europeans—yet he has also slapped tariffs on them. He wants to sign a nuclear-disarmament deal with North Korea; to do that, he needs the active help of China and South Korea—yet he’s … you get the idea.

Even with leaders whom he has tried to befriend, he hasn’t done so in ways that give him leverage. Russian President Vladimir Putin has corrupted U.S. elections, poisoned exiles in allied nations, and abetted mass killings in Syria—all to no objection from Trump. But now that Trump has an opportunity to exert some pressure over Russia’s recent naval aggression against Ukraine, he’s backed away; he canceled a one-on-one meeting he and Putin were scheduled to hold at the G-20. He canceled the session ostensibly as a protest against Russia’s actions. But a protest would have been more potent if he had held the meeting and made the U.S. position clear, especially since our position on Russia isn’t clear at all. Trump’s Cabinet secretaries and U.N. ambassador denounce Putin for one thing or another, but Trump says little, often contradicting his experts, leaving Putin with the sense that he might get away with whatever he wants to do.

One likely explanation is that Trump didn’t want to have a meeting where he would have to criticize Putin.

And here, special counsel Robert Mueller’s investigation comes into play. Just before the summit, Trump’s former lawyer Michael Cohen revealed that his client was angling to build a Trump Tower in Moscow, even offering Putin the $50 million penthouse apartment, at the same time that he was running for president, promising to restore good relations with Russia if elected and telling his crowds that he had no business deals in that country. This is the blackmail that Putin may have been holding over Trump all along. Quite aside from the scuzzy (and possibly impeachable) nature of this relationship, it precludes Trump—and prevents the United States—from having a coherent policy toward Russia, from dealing with any threats (or opportunities) that Putin poses.

The same may be true of Saudi Arabia, where Trump has also pursued investments. Crown Prince Mohammad bin Salman—who is also at the G-20—ordered the brutal murder of journalist and U.S. resident Jamal Khashoggi), but Trump has firmly stood by him, no strings attached, even waving away the CIA’s assessment that MBS was involved.

The one thing Trump might accomplish this weekend is averting a trade war with China. This could be the summit’s banner headline, depending on the outcome of a one-on-one meeting, scheduled for Saturday, with Xi. If the meeting goes well and Trump assents to holding additional talks, rather than imposing steeper tariffs on Chinese goods, he will only be averting a crisis that he created. Of course, the outcome could go the other way: Trump may decide against further talks, thinking he could squeeze more out of Xi by piling on more tariffs or threatening to do so—a risky tactic, as Xi might not scream but rather escalate the conflict.

Either way, Trump is going into these talks awfully nonchalantly. “China wants to make a deal,” he said at the same Mar-a-Lago press conference where he touted the wisdom of his gut. After all, he and Xi have a “great relationship,” he boasted. “I like him a lot. I think he likes me.”

Trump doesn’t get it. First, the two of them don’t have a great relationship. Second, friendship among leaders can boost the prospects of a deal if they share interests, but not if they don’t, and it’s unclear which interests either Trump or Xi is willing to compromise in order to get a deal at the moment. The decisive factor may be whether Trump takes the advice of his chief economic adviser, Larry Kudlow, his trade negotiator, Robert Lighthizer, or his director of trade policy (and author of Death by China), Peter Navarro. The three disagree over tariffs, and, as Trump boarded Air Force One for the 11-hour flight to Buenos Aires, he hadn’t yet taken sides.

There’s the nub of the matter: Trump is going into high-level talks that may determine U.S.-China relations, the jobs and fortunes of millions of Americans, and the shape of the world economy for the next few years—and he doesn’t have a grasp of what U.S. policy should be or even what U.S. interests are. He doesn’t satisfy the most basic definition of a national leader, much less a world leader.