Xi Jinping came into the meeting fully prepared and well-versed in all of the critical trade disputes. He was open to finding solutions and made clear that China is even flexible on the issue of intellectual property protections, a big part of the Trump-Lighthizer agenda. While USTR Robert Lighthizer and Treasury Secretary Steve Mnuchin are leading the US negotiations and Liu He is leading the Chinese team, the summit meeting made clear that it is actually Xi and Trump who will be leading the effort.
One of the factors in the relative success of the summit was the clear understanding on the part of both leaders that a further erosion of US-Chinese relations, particularly economic relations, would be bad for both countries and even worse for the global economy. The months of tit-for-tat sanctions and other punitive measures have already slowed down global economic growth, and a full-blown failure of the Buenos Aires talks would have rapidly made matters worse.
The outcome of the 2-and-a-half hour meeting and dinner between Trump and Xi was an agreement to negotiate in good faith. China pledged to buy more American products, including agricultural products as a way of reducing the trade imbalance. Trump froze the expanded tariffs, scheduled for January 1, 2019. The handshake between Trump and Xi was similar to previous handshakes with EU's Jean-Claud Juncker and with Japanese Prime Minister Shinzo Abe. So far the only full-blown trade deal is the USMCA with Mexico and Canada. But in the European Union and Japanese cases, the agreement to negotiate in good faith halted escalating tariffs and set a good framework and mindset for negotiating. Good enough for starters.
Now the hard work begins. The initial 90 day period for negotiating a substantive trade agreement, eliminating all of the existing tariffs and other trade barriers is really a much shorter period of time. Both the US and China have holidays that will interrupt the negotiating. Both sides need time to prepare, and if the talks succeed, both sides will need time to present the outcome and establish a consensus.
The fact that much still needs to be done does not in the least change the assessment that the Trump-Xi meeting was an important step. Previous US Administrations let China continue its unfair trade practices without a whimper. There were consequences to that vacating of US leadership. Trump has made clear that the past business as usual cannot continue. There is begrudging international consensus that he is right, even though European leaders are very wary of giving Trump much credit.
Both Trump and Xi face extremist elements that don't want any rapprochement between Washington and Beijing, and who believe that conflict is inevitable and their side will emerge victorious. A failure of the summit in Argentina would have bolstered those factions in both countries, and that would have had very dangerous consequences.