Shortly before President Trump met Chinese leader Xi Jinping in South Korea, an urgent issue emerged. Trump wanted to discuss a request by Nvidia Chief Executive Jensen Huang to allow sales of a new generation of artificial-intelligence chips to China, current and former administration officials said. Greenlighting the export of Nvidia’s Blackwell chips would be a seismic policy shift potentially giving China, the U.S.’s biggest geopolitical competitor, a technological accelerant. Huang—who speaks to Trump often—has lobbied relentlessly to maintain access to the Chinese market...