Amidst rising tensions in Northeast Asia, U.S. Secretary of State Rex Tillerson’s upcoming visit to the region this week offers a glimmer of hope that diplomacy could avert a military conflict with North Korea.

For Tillerson, this will be the toughest test of his diplomatic skills. The odds that the secretary of state’s trip will cobble together a regional coalition to contain Pyongyang’s nuclear and missile ambitions do not appear good. South Korea has plunged into political chaos after the recent impeachment of President Park Geun-hye. Its political elites are deeply split over North Korea, which Tillerson is expected to visit on Friday. Japan, America’s staunch ally where Tillerson is expected to make his first stop Wednesday, will likely provide unreserved support. In China, Tillerson will almost certainly find his toughest interlocutors when he visits next weekend.

To Washington, Beijing’s response to Pyongyang’s brinksmanship has long been a source of frustration. As North Korea’s patron, only China has the means to pressure the Kim Jong-un regime to moderate its behavior. To be sure, in recent years Beijing has taken some modest measures trying to rein in Pyongyang. For example, China has supported sanctions against North Korea at the United Nations Security Council. Last month it also announced the suspension of coal imports from North Korea.