The annual United Nations General Assembly in New York this week felt like the center of the world, but it was ultimately overshadowed by a meeting in Washington where President Trump hosted President Xi Jinping of China at the White House. The summit offered a sharp contrast with the faltering U.N. in a gridlocked New York.

Mr. Trump and Mr. Xi met at a moment when their countries wield huge power over the global economy and the future of technology. The U.N. is faltering, dysfunctional and largely ineffectual as world powers increasingly circumvent or ignore it. It was telling that Mr. Xi did not bother to stop in New York on his way to see Mr. Trump.

The global body, founded in 1945, has been paralyzed by divisions on the U.N. Security Council. Disputes involving the United States, China and Russia have blocked substantive action on matters like conflicts in Iran, Ukraine, Gaza, Yemen and South Sudan. Mr. Xi has real power in Ukraine and Iran.

The secretary general of the U.N., António Guterres, led a discussion on global governance of A.I., but many experts concede any meaningful near-term effort to ensure the technology does not escape human control likely requires an agreement between Washington and Beijing.