For Trump, these forums can be tiresome. He has made no secret of his contempt for multilateral institutions and the ponderous deliberations that define them. But the gathering in Buenos Aires will also serve as the backdrop for a potentially fascinating series of face-to-face encounters between leaders wrestling with their own political challenges. Military standoffs, lurid assassinations, sweeping trade wars and brewing financial crises all loom over proceedings.

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“The once snooze-worthy global power fest now looks like diplomacy on steroids,” observed CNN’s diplomatic editor, Nic Robertson.

Still, Trump’s hosts are hoping for a calmer gathering than the spiky affair that took place in Hamburg last year. “The Argentines are trying to minimize topics that could trigger Trump’s Twitter finger — including protectionism, the Paris climate agreement, and migration,” my colleagues reported. “In the declaration issued at the end of the summit — in which leaders sum up their work and set priorities for their underlings — Argentina is working hard to minimize U.S. embarrassment.”

Things have not gotten off to a promising start. Stung by new revelations from the special counsel investigation into his campaign’s dealings with Russia, Trump’s team announced from Air Force One that it would suspend or downgrade a number of formal bilateral meetings in Buenos Aires, including scheduled sit-downs with the leaders of Turkey and South Korea.

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But even if the president plays a more circumspect role than in the past, he’s far from the only person to track this weekend. Here are the leaders to watch:

Vladimir Putin — A week ago, all eyes were on the Russian president’s anticipated meeting with Trump. It would have been the follow-up to their July summit in Helsinki, where Trump incensed observers on both sides of the Atlantic with his seeming deference to Putin.

But the crisis sparked over the weekend in the Sea of Azov, where Russia seized three Ukrainian vessels and their crews, eventually compelled Trump — after a fair amount of dithering — to call off the session.

Kremlin officials shrugged off the news. “If this is indeed the case, the president will have a couple of additional hours in his schedule for useful meetings on the sidelines of the summit,” said Putin spokesman Dmitry Peskov.

Mohammed bin Salman — As we wrote yesterday, no world leader will be watched more closely than the Saudi crown prince, who comes to the G-20 under a dark cloud of international scrutiny. Trump may be eager to absolve Mohammed of his role in the abduction and assassination of journalist Jamal Khashoggi, but other leaders are less keen to sweep the whole episode under the rug.

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British Prime Minister Theresa May deemed the Saudi explanation for Khashoggi’s killing — which pinned the blame on rogue actors in his palace — not credible. German Chancellor Angela Merkel’s government halted all new arms sales to Riyadh and banned more than a dozen Saudi officials implicated in the crime from traveling to Germany. Turkish President Recep Tayyip Erdogan has loudly inveighed against the Saudis for the murder, which took place at the Saudi consulate in Istanbul, and has accused Riyadh of engaging in a coverup.

“The question is who among global leaders will agree to stand with him publicly,” said H.A. Hellyer, a senior fellow at the Atlantic Council and the Royal United Services Institute in London, to Agence France-Presse. “I suspect his appearances will be carefully staged to avoid embarrassment.”

But the G-20 may offer the crown prince a chance for redemption: He is set to meet Putin and French President Emmanuel Macron at the least. Both leaders have said they would raise Khashoggi’s death with Mohammed, but Saudi officials in the kingdom hope such meetings will help their leader restore some goodwill.

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Xi Jinping — The weekend’s clash of the titans will be a Saturday meeting between Trump and his Chinese counterpart. Trump, riled by China’s “unfair” trade practices, has instigated a trade war with Beijing over the past year. Talks between the two sides have sputtered in recent months and Trump threatened this week to raise tariffs even higher on Chinese imports.

Analysts hope that cooler heads will prevail. “I think it’s in President Trump’s interest to have this meeting be viewed as a success,” said David Dollar of the Brookings Institution, in a phone conference this week with reporters. But it’s unlikely Xi will give Trump the concessions the White House has long sought from Beijing, so the likelihood of a meaningful truce is slim.

Justin Trudeau — The Canadian prime minister locked horns with Trump at the tumultuous Group of 7 summit held in Quebec earlier this year. Trudeau branded then-new U.S. tariffs as “unacceptable actions”; Trump cited Trudeau’s comments as the reason for refusing to sign on to the summit’s customary joint communique. But this Friday, the two leaders may meet to sign a new trade agreement between their countries and Mexico, the product of months of fitful negotiations.

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The optics will be tricky for Trudeau. “These summits are very much about sending a pretty picture to the people back home, and Trudeau might not want to appear to stand side by side with Donald Trump not knowing what mood the president is going to be in,” said John Kirton, the director of the G-7 and G-20 Research Groups at the University of Toronto, to Canada’s CBC News.

Mauricio Macri — The victory of Argentina’s center-right president in 2015 was supposed to be a sign of a growing trend in Latin America — a pragmatic businessman beating an increasingly unpopular leftist government. But in Brazil and Mexico, the other Latin American powers in the G-20, a far-right hard-liner and leftist populist are now about to take power after seismic electoral wins this year. Macri has to adjust to a shifting and increasingly polarized political climate in the region.

“As the central portion of the triangle — the one that’s neither right nor left, that deliberately occupies the space in between — Macri can send a message of moderation, and champion cohabitation as an alternative to the social and political rift that is becoming more dangerous by the day,” noted an op-ed in Argentine daily Clarin.

But that’s no easy task — especially at a time when Macri’s biggest challenge is a financial crisis at home that is expected to generate mass protests over the weekend.