Call it the "North Korea challenge trip."

President Trump embarks Sunday on a 13-day visit to Asia that will be the longest journey by any U.S. president since 1991, when George H.W. Bush ended a lengthy Asia tour by vomiting at a state dinner in Tokyo and falling into the Japanese prime minister's lap.

Trump aides are reportedly working hard to prevent any such disasters, including unscripted comments and tweets. "There are going to be a lot of white knuckles on this trip," says Council on Foreign Relations Korea expert Scott Snyder. "They want him to stay on script."

But the most urgent agenda item as Trump swings through Japan, South Korea, China, and Southeast Asia will be ratcheting up the pressure on North Korea to end its nuclear program. "The president recognizes that we're running out of time and will ask all nations to do more," the White House national security adviser, H.R. McMaster, told reporters.

Yet North Korea is the subject that inspires the most reckless presidential rhetoric and tweets, which some fear could spark an unintended conflict. So the most riveting feature of the Trump trip will be whether the president chooses to goad North Korean leader Kim Jong Un or vice versa while he is traveling.

Trump and Kim's ongoing game of North Korea roulette could get even hotter.

Here are the signs to watch for as Trump ventures abroad:

One. Take note of the pomp and ceremony. There will be lots of it, as leaders try to feed Trump's ego and distract from disagreements. In Japan, Prime Minister Shinzo Abe will try to cement his relationship with Trump and sideline dissent over trade on the golf links. There will be a formal meeting with the Japanese emperor and adulation for Ivanka. But Japanese journalists are not shy and may ask pesky questions about U.S. willingness to attack North Korea.

In Beijing, says the Council on Foreign Relations' China expert Elizabeth Economy, Trump will get the full red-carpet treatment to distract attention from trade issues. "The Chinese will announce some deals, but the big issues won't be resolved," she says. China will keep Trump's visit tightly controlled in an effort to hide tensions over whether China is doing enough to curb North Korea.

Two. Observe the dynamics between Trump and Chinese President Xi Jinping.Trump has made clear that he views his China trip purely as a confab between two strongmen and has bragged about his close relationship with Xi. His main focus will be on North Korea.

But "Trump's affection for Xi is largely one-sided," says Economy. Moreover, "their relative standing couldn't be more different." Trump comes into their meetings weakened by low ratings and the Russia investigation, while Xi is just coming off a party congress where his vast powers were strengthened.

Meantime, Trump's withdrawal from multilateral trade deals and his hot-headed rhetoric on North Korea have left regional leaders wondering whether he is capable of handling Beijing or Pyongyang. Those leaders will be avidly assessing how Trump and Xi match up.

Three. Watch whether Trump gets any commitment from Xi to tighten banking and oil sanctions on North Korea. To the administration's credit, the Chinese have now imposed more serious sanctions than ever before on North Korean businesses, workers, banking access, coal exports, and oil supplies. And there is an ongoing debate inside China about whether even tighter sanctions should be applied.

But none of the experts with whom I spoke believed Xi would endorse additional sanctions during Trump's trip. "China will take the position that the ball is in the U.S. court, and it is time for Washington to try negotiations with Pyongyang," says the Atlantic Council's Alexander Vershbow, a former U.S. ambassador to NATO. However, Washington has unrealistic preconditions for talks, as does Pyongyang.

Moreover, Kim seems committed to perfecting his intercontinental ballistic missile before he would be willing to consider bargaining. "They want a credible ICBM and are in no rush to talk," says Leland Miller, a China expert at the Atlantic Council. This leaves Washington and Pyongyang in an unavoidable cycle of escalation unless China steps in.

Four. So, watch to see whether a miracle happens — Trump and Xi come up with a joint policy that might lead to renewed nuclear talks with Pyongyang.

Here is where really skilled diplomacy might make a difference, if Trump believed in it or had a secretary of state empowered to do the job. That would require the president to make credible threats to China in private — like  imposing secondary sanctions on Chinese banks — while refraining from incendiary tweets.

And it would require minimal agreement with Beijing about the purpose of sanctions. Presumably, they are meant to drive Kim to the bargaining table, but what would be the goal of negotiations? At this point, North Korea is already a nuclear power, and limitation of its nuclear program might be the only realistic endgame.  Would Washington accept that?

A snowball in hell probably has better prospects than a serious Trump effort at diplomacy, and he may leave empty-handed. The likely alternative is a return to verbal escalation between Kim and Trump that may lead to North Korea testing more missiles or even an atmospheric nuclear test.

Therefore, the main thing to watch for on Trump's trip may be whether it can be completed without another round of North Korea roulette.