The second summit between US President Donald Trump and North Korea n leader Kim Jong-un ended in Hanoi on Thursday. The White House, in a statement, said no agreement was reached but the two leaders had "very good and constructive meetings." It emphasized their respective teams "look forward to meeting in the future." The results have fallen short of expectations, leading to wide disappointment.Trump told reporters that the US "couldn't give up all the sanctions" as North Korea demanded, insisting sanctions could only be relaxed after North Korea denuclearized.The two are deadlocked again over an old problem: The US demands North Korea denuclearize first, while the latter insists on prioritizing the lifting of sanctions. The two cannot reach an agreement on working simultaneously to achieve the same goal.The détente between Pyongyang and Washington failed to help the two countries get rid of deep mutual distrust. That the Trump-Kim summit ended with no fruition indicates it's difficult to advance the denuclearization process of the peninsula. It can't be fulfilled in a short time.Expectations for the setting up of liaison offices and the declaration of a formal end to the Korean War have fallen apart. What's most important for the two countries is to cherish the results achieved so far and not back down from one setback.Washington's attitude is the key. "I very much appreciate no testing of nuclear rockets, missiles, any of it," Trump said earlier in Hanoi. "Speed is not that important to me." After the meetings, Trump noted his talks with Kim didn't end in quarrels but in "a friendly walk." Whether such an attitude can be sustained in the future is facing a test.Some Americans will criticize Trump for the alleged failure of his North Korea policy. If there is still no new progress on peninsula denuclearization, the president will face increasing pressure.With the approach of the US presidential election, these pressures will force him to take a tough attitude toward Pyongyang again.China and South Korea should play a role in safeguarding the achievements made so far concerning the issue. Pyongyang announced it would permanently halt nuclear and missile tests before the US and South Korea suspended joint military exercises. Beijing should help Pyongyang stick to its current moderate line while Seoul should firmly resist any Washington attempt to coerce North Korea with threats of resuming joint drills. South Korea should take a responsible role in maintaining the peace of the Korean Peninsula The most effective way to stabilize the Korean Peninsula is to push North Korea and the US to move toward each other and try to promulgate a dual-track road map of denuclearization and peninsula peace that can be accepted by both.It's particularly important to be optimistic at this critical moment. The Korean Peninsula was in great uncertainty in the latter half of 2017, but now there are neither nuclear tests nor joint military exercises.Trump and Kim have met twice. Even if no deal was reached, both vowed not to cease negotiations. This is a big change.No power should disrupt the reconciliation process on the peninsula. China will never accept any retrogression. This is our bottom line to which we will firmly stick. We hope South Korea will continue to cooperate with us. The US and North Korea shouldn't frustrate the whole region and the international community.