And some signs have been positive. China announced in February that it would ban North Korean coal imports — which account for 40% of the country’s total exports to China — for the rest of 2017, in line with existing United Nations sanctions. Chinese experts have said that Beijing could halt crude oil exports to North Korea should Pyongyang test a nuclear weapon (it has carried out five nuclear tests since 2006 and could soon conduct another).

Yet the picture is far from clear. Visitors to the Chinese-North Korean border have witnessed coal trucks crossing, suggesting that the ban hasn’t been fully implemented. North Korea’s exchange rate has held stable, suggesting that its economy hasn’t taken a dive. And China’s trade with North Korea grew nearly 40% in the first quarter of the year, according to Chinese official figures.

Maybe Trump is “trying to shame, or guilt, or flatter Xi into doing something,” said Robert Kelly, a professor of political science at Pusan National University in Seoul. “But the Chinese are craftier than that. They’re playing the long game on this one — they’re thinking of the next 20 or 30 years. That’s why this stuff isn’t going to work — it’s not how the Chinese make these kinds of decisions.”