It was drizzling rain, and gloomy clouds darkened the surface of the Yalu River separating this Chinese city from its North Korean neighbor.

The men, and a handful of women accompanying them, slipped in and out of storefronts to buy cosmetics and other personal items to take back home. More important, they paid inconspicuous visits to the offices of trading firms that account for part of the vital flow of goods between China and North Korea.

The presence of these visitors was a small but telling sign that China’s critical role in the punishing international embargo on trade with Pyongyang — an embargo the Trump administration is counting on to force North Korea to stop building nuclear weapons — seems to be breaking down.

After his dramatic summit meeting with North Korean leader Kim Jong Un in June, Trump declared on Twitter, “There is no longer a Nuclear Threat from North Korea.”