While Trump canceled his meeting with Putin, the US president was still scheduled to meet with Chinese President Xi Jinping, but analysts were not optimistic about prospects for a major breakthrough on the two countries' trade disputes a month before USA tariffs on Chinese goods are set to ramp up.
In November, Asia Pacific Economic Cooperation officials gathered in Port Moresby, Papua New Guinea, failed to issue a joint statement for the first time ever after the USA and China delegations clashed over language addressing trade and security.
British Prime Minister Theresa May lauded the late Bush as "a great statesman and a true friend of our country", words that few observers in Britain would apply to Trump.
The Kremlin said it had not been notified and only learned about it from the tweet.
Merkel's spokesman said that during a meeting with Russian President Vladimir Putin, she also voiced concern about rising tensions in the Kerch Strait off Crimea and pushed for "freedom of shipping into the Sea of Azov".
The two countries are also at odds militarily over China's extensive claims in the South China Sea and US warship movements through the highly sensitive Taiwan Strait. Their countries have been embroiled in an escalating trade war with new US tariffs on China goods set to take effect a month from now.
Trump has criticized the WTO and taken aggressive trade policies targeting China and the EU.
Growing concerns that the trade war will increasingly hurt corporate earnings and the US economy are a key reason why USA stock prices have been sinking this fall.
China, in response, is threatening to impose taxes on an additional 5,000 types of American imports worth about $60 billion.
"Donald, it is all the more reason we need to keep working to remove the steel and aluminum tariffs between our countries", Trudeau said. If we can make a deal that'd be good.
"Willis Sparks, director of global macro politics at Eurasia Group, said: "Just to see how leaders interact with the crown prince will be interesting - how warm they are".
"We are in a bad situation, and we're putting a pile of money into this?"
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Laura Jaitman, the Argentine Treasury official shepherding the G-20′s financing talks, said leaders have made progress on finance and trade and was hopeful a joint statement would be possible.
The stakes are high for the world's two biggest economies.
But in a rhetorical olive branch to Trump, Xi pledged to do more to open up China´s economy. He said he hopes China will criminalise fentanyl, the synthetic form of opioids largely shipped from China.
Including a commitment to currency, transparency is seen as a precedent set by the Trump administration for negotiating with countries that have a history of manipulating their exchange rates.
"But in terms of doing a deal. that's entirely up to the president of the United States and the president of China".
"Should there be any other aspirations, such as taking advantage of the trade spat to throttle Chinese growth, then an agreement is unlikely to be reached", the newspaper said in an editorial Friday.
The state-run China Daily said Friday that both sides could find a deal in Buenos Aires but warned the United States against pushing too hard on technology, amid USA accusations of widespread theft by Beijing.
"Instead, leaders buried their differences in obscure language and dropped language to fight protectionism, which had been included in every G-20 communique since the leaders' first summit", he said.
The revamped accord, called the US-Mexico-Canada Agreement (USMCA), looks a lot like the one it replaces.
Two major summits this year, of the Group of Seven democracies and the Asia-Pacific Economic Cooperation forum, ended without the once-routine statements. "This is clearly a retrograde step forced by United States intransigence".
On Friday Mr Trump briefly met Russian President Vladimir Putin on the sidelines of the G20, a Russian official told Reuters.