Donald Trump has become the wrecking ball of the postwar global order—and he clearly revels in its destruction. Yet nearly two years into his Presidency, he is still struggling to translate his so-what-if-no-one-else-does-it-this-way initiatives into tangible foreign-policy feats. So far, he has little to show on big-ticket challenges, including Russia, China, North Korea, Middle East peace and Iran, international trade and tariffs, or arms deals. His next big test is this weekend, in Buenos Aires, at the G-20 summit, convening the world’s largest economies and weightiest powers. All of those issues will be on his agenda in one venue.

The Administration still feigns high hopes. On Thanksgiving, Trump—who recently gave his Presidency an A-plus—said he is confident about his prospects at the G-20 summit, including negotiations with China’s President, Xi Jinping, to avoid a trade war. “I’m very prepared,” he told reporters. “You know, it’s not like, ‘Oh, gee, I’m going to sit down and study.’ I know every stat. I know it better than anybody knows it. And my gut has always been right.”

Others, including former diplomats involved in former G-20 meetings, aren’t so optimistic. “Given President Trump’s fixation on muscular unilateralism, and dismissiveness toward diplomacy, it’s a safe prediction that this will likely be a missed opportunity, at best, and an accelerator of disorder, at worst,” William Burns, a former Ambassador to Russia and Deputy Secretary of State, who is now president of the Carnegie Endowment for International Peace, told me. “The President tends to behave at such events like a bull with his own china shop in tow, intent on disruption for its own sake.”

Burns said that Trump’s limitations are his “autocrat-envy” and his transactional approach to diplomacy—at the expense of global unity or traditional American values.

“The likely result, like so much of the rest of U.S. policy over the past two years, is to leave allies uncertain, adversaries emboldened, and international order still more fragile,” Burns, the author of the impending “The Back Channel: A Memoir of American Diplomacy and the Case for its Renewal,” told me.

Trump has never liked the big summits anyway. “He generally hates all of them, because he knows most of the leaders don’t like him personally and feels ganged up against in these multilateral formats,” Ian Bremmer, the president of the Eurasia Group, told me. Trump recognizes that he’s a political outlier among most of the other leaders attending from countries on six continents, ranging from Argentina to Australia, Canada to China, South Africa to South Korea. Only the governments in Italy and Brazil have openly embraced Trump-style nationalism, Bremmer noted.

Recent events have deeply complicated the prospects of Trump emerging from the G-20 with a diplomatic breakthrough. “This year’s G-20 comes against the backdrop of a disordered international landscape—more crowded, contested, and complicated than at any time since the inception of the group two decades ago,” Burns said.

Trump’s trip to the G-20 meeting was supposed to be the place to plot a future course with President Vladimir Putin after their largely unproductive summit, in Helsinki, in July. But new Russian aggression against Ukraine—firing at three Ukrainian naval boats, then seizing the vessels and crews, on Sunday—has escalated dangers of a full-blown conflict between the two countries. On Monday, Ukraine responded by declaring martial law to allow rapid mobilization of its military forces. More than eleven thousand people have died since Russia invaded and annexed Crimea in 2014 and increased arms and aid to separatists in Ukraine’s eastern Donbass region. The new tensions led Trump to rethink the Putin talks. “Maybe I won’t even have the meeting,” Trump told the Washington Post, on Tuesday. “I don’t like that aggression at all.”

At an emergency session of the U.N. Security Council on Monday, the U.S. Ambassador, Nikki Haley, charged that Russia had engaged in “outlaw actions” in confronting the Ukrainian Navy at the Kerch Strait, which is between the Black Sea and the Sea of Azov. The United States would welcome a normal relationship with Russia, she said, “but outlaw actions like this one continue to make that impossible.” Further, Russian escalation “will only make matters worse,” she warned. On Wednesday, Ukraine claimed that Russian forces—hundreds of war planes and attack helicopters as well as “battalion-tactical groups” of troops—were massing along the Ukrainian border. Russia announced that it would deploy additional S-400 anti-aircraft missiles to the Crimean Peninsula by year’s end.

Trump has long sought to better relations with Putin. He now faces unappealing options whatever he does. “Undoubtedly, briefings for the President in the run-up to the G-20 will accentuate Russia’s renewed aggression. The question is what he does with this. Does he confront Putin or not?” William Taylor, the former U.S. Ambassador to Ukraine and now the executive vice president of the U.S. Institute of Peace, told me.“If the President doesn’t act, it tells Putin that he can get away with it again—that the international community will not stand up for the Ukraine and not oppose further aggressive acts by Russia.”

The President also has to weigh the cost-benefit of holding a second summit with Putin amid the Mueller investigation into Russia’s meddling in the 2016 election. He will have to be careful amid intense media coverage of the Mueller investigation and the impending sentencing of Paul Manafort, Trump’s former campaign manager. “With all the problems that he has on this Mueller investigation, the President knows that for him to be seen to be making deals with or compromising with or supporting Putin is awkward,” a former senior diplomat told me. “It strengthens the argument that he is compromised by the Russians.”

Whatever Trump decides, new Russian aggression “has made it harder to pursue the kind of bromance with Putin that Trump has established with Kim Jong-Un,” Alexander (Sandy) Vershbow, the former Ambassador to Russia and South Korea and the former deputy secretary-general of NATO, told me. “The real problem is Trump’s inability to see any threat to U.S. interests in Putin’s flagrant violations of Ukraine’s sovereignty (Obama’s fault), his interference in U.S. and other elections (a hoax), or his attempted assassination of political enemies on the territory of our closest NATO allies. (He hasn’t done it on American soil, so who cares.) Trump attaches no importance to the rules-based system Putin aims to undermine.” As a result, Putin “sees nothing but weakness and lack of principle and has no reason to change his disruptive behavior,” Vershbow added.

Trump’s most important meeting may be with his Chinese counterpart, over dinner, on Saturday night. Again, issues of war and peace—over tariffs—are at stake. Experts and former envoys generally think the most likely outcome is a temporary tariff ceasefire so that new U.S. tariffs—or any Chinese tit-for-tat response—goes into effect on January 1st, as currently scheduled. In an interview with the Wall Street Journal, the President signalled on Monday that he is “highly unlikely” to delay an increase in tariffs.

But Trump has been rattled by the G.M. announcement this week of about fourteen thousand layoffs and recent stock-market plunges that threaten to wipe out gains for 2018. “The Xi meeting is the big open question,” Bremmer told me. “Trump has most recently poured cold water on any breakthrough on tariffs. But the meeting has been set up to make progress.”