Part of the reason China was willing to take a harder line against North Korea was to curry favor with the U.S., but Trump has proposed tariffs on Chinese exports anyways, ratcheting up trade tensions.

Why it matters: Beijing is now reassessing its priorities when it comes to North Korea, according to Jenny Town, managing editor of 38 North, and may be less willing to keep up the pressure.

Between the lines

Obviously China has other motivations in sanctioning North Korea, Town says: “they were frustrated with North Korea and they don’t want North Korea to have nuclear weapons.” But this trade war changes the calculus in Chinese-U.S. relations, including on North Korea.

That's especially true given that Trump himself suggested in a NYT interview he would reconsider trade issues with China given its stance on North Korea:

"China...If they’re helping me with North Korea, I can look at trade a little bit differently, at least for a period of time. And that’s what I’ve been doing."

— Trump in December, 2017

China's calculus

Robert Manning, a former senior strategist with the Office of the Director of National Intelligence under Barack Obama, says China's "concern for stability" informs the reluctance to pressure North Korea. They're worried "if they squeeze too hard," they could help precipitate a "collapse," he says.

That is threatening to the Chinese for two reasons, per Manning. One, "the Chinese understand that missiles can be pointed in all directions," including at them, and they also share a border which, in the case of collapse, could mean a humanitarian crisis in Chinese territory.

What's next?