My first in-depth interaction with Tung Chee Hwa came at a time of crisis. In April 2001, an American EP-3 spy plane had just collided with a Chinese military jet and was forced to make an emergency landing in Hainan Island. At the time, I was running a Morgan Stanley investment tour of China for about fifteen of the world’s most prominent and deep-pocketed investors, most of whom had never been to China before.

The summit showed that differences can be bridged on competitive issues such as AI governance, trade stability, climate change, public health and transnational crime. That that bridge can model ways of working together that can help solve other problems.

At the Washington summit it was more than obvious that China-U.S. cooperation is essential and must continue despite any potholes in the road. Neither country, nor the world, can afford to have the wheels come off.

The May and September reciprocal state visits by U.S. President Donald Trump and China’s President Xi Jinping have seemingly succeeded in cementing warm personal ties between the two leaders while stabilizing an unstable U.S.-China relationship. Historians may look back on these twin summits as perhaps a turning point following a decade of tumult and steadily intensifying competition between the two powers. While the two summits have succeeded in warming the atmosphere, there remains much substantive and institutional work to do.

The upcoming Trump-Xi summit may yield few concrete breakthroughs, with much about both the substance and presentation of the meeting still uncertain. Maintaining the relative stability achieved at their last meeting in Beijing may be the central outcome as the two sides navigate continuing differences over trade, rare earths, artificial intelligence and other issues.

The United States needs to demonstrate solidarity with Japan as it faces concurrent challenges from China, Russia, and North Korea.

The upcoming Xi-Trump summit could yield progress on trade, AI and other areas, but deeper tensions will remain. Its significance may ultimately lie in three areas: stabilization, substance and symbolism.

Whether it be the rise of right-wing populism, a sweeping expansion of presidential power, an assault on liberal pluralism or a transactional approach to alliances, it’s clear that Donald Trump and his supporters are attempting to change key underlying assumptions about what America is.

The relationship is likely to remain characterized by the dynamics of cooperation and competition—with friction and coordination coexisting for the foreseeable future. The primary role for heads of state will not be to produce dramatic breakthroughs but rather to build trust.

The news of the passing of Mr. Tung Chee Hwa — former Vice Chairman of the National Committee of the Chinese People's Political Consultative Conference (CPPCC), the first Chief Executive of the Hong Kong Special Administrative Region (HKSAR), and Founding Chairman of the China-US Exchange Foundation — reached me on September 8. Although I knew that Mr. Tung was very ill for quite some time, yet I was sadly struck by this grievous news. With his departure, I have forever lost a respected leader, mentor and trusted friend. My mind is flooded with reflections on his contributions to think tank development, international exchange and national service, and I find myself unable to contain my grief while writing these lines to recall my days with him personally in the past 20 years.