Richard Armitage, president of Armitage International, was deputy secretary of state from 2001 to 2005. Victor Cha, a senior adviser at the Center for Strategic and International Studies (CSIS) and a professor at Georgetown University, was director for Asian affairs on the National Security Council staff from 2004 to 2007. Michael Green, senior vice president for Asia at CSIS and an associate professor at Georgetown, was senior director for Asian affairs on the NSC staff from 2001 to 2006.

President Obama has promised to rebalance U.S. foreign policy to the Asia-Pacific region. It did not help that he had to cancel a trip to the region in October so that he could deal with the government shutdown, but the White House made the right move by announcing that he would make up for it with a trip in April.

The full itinerary has not been announced, but Obama is expected to visit Japan, the Philippines and Malaysia. Those stops make sense: Japan is the biggest U.S. ally in the region; our ally the Philippines was clobbered by Typhoon Haiyan and needs reassurance in the face of Chinese pressure over territorial disputes; and Malaysia is emerging as a major trade and potential diplomatic partner. The president held a long summit with Chinese President Xi Jinping last summer in California and will travel to Beijing in the fall for a regional summit, so there is no need to go to China this time.

So what about South Korea?

Visiting key treaty allies Tokyo and Manila, while skipping another key ally, South Korea, on Obama’s first trip to Asia of his second term would be an embarrassment for South Korean President Park Geun-hye, particularly given how prickly relations are between Tokyo and Seoul. If anything, North Korean threats and Chinese muscle-flexing should put a premium on Obama ensuring that our two democratic allies in North Asia not work against each other. We have worked at senior levels in the National Security Council and State Department, and we recognize that one of the most precious commodities in Washington is the president’s time. We would not recommend that Obama try to arbitrate the complex historical problems between Japan and South Korea. But this trip is the ideal opportunity to keep the leadership in Tokyo and Seoul focused on what we can and must do together in the future.

Developments on the Korean Peninsula are at a critical juncture. The United States is to transition wartime operational control of all forces in the South from a U.S. general to a South Korean general next year under an agreement reached by previous South Korean governments. Park’s government worries that North Korean uncertainties make this an undesirable time to switch over and that Washington’s next move might be to withdraw U.S. forces from the peninsula. The Pentagon worries that Seoul seeks a delay to avoid earlier promises to pay for more of the nation’s defense. A new agreement would raise Seoul’s annual contributions to the costs of U.S. forces based in South Korea to about $866 million. But the Korean National Assembly is likely to debate this amount hotly, and Park’s government would need to demonstrate the strength of the alliance and the U.S. commitment before the Korean fiscal year ends this spring.

North Korea, China, Japan and Russia are watching. The absence of consensus on these military issues creates strategic uncertainty and requires presidential attention.

Separately, time is running out for the United States and South Korea to negotiate a new civil nuclear cooperation agreement before the current pact expires. The two are at loggerheads over Seoul’s demand that it have the right to enrich uranium on the front end of the fuel cycle and to reprocess spent nuclear fuel on the back end. Washington believes that enriched uranium fuel is plentiful enough on the open market for the South to acquire. The international nonproliferation community is also concerned about the precedent that would be established by allowing Seoul to acquire a full nuclear fuel cycle.

April is also critical timing for trade negotiations. Seoul is interested in “docking” the U.S.-South Korea free-trade agreement into the broader Trans-Pacific Partnership being negotiated by the United States and 11 other countries. Korean participation in the partnership would further cement a future trading order in Asia that would include North America and drive exports for U.S. workers and farmers.

Finally, North Korean activities suggest that by the time Obama would arrive in Seoul, the North would have engaged in yet another dangerous provocation. It could be a nuclear test — possibly one revealing that Pyongyang has increased the kilotonnage of its plutonium-based weapons or successfully tested a uranium-based weapon. Or it might be another long-range missile launch or shelling of islands off South Korea’s coast. Whatever the provocation, the United States would need to demonstrate solidarity with Seoul and galvanize regional pressure to deter further escalation by Pyongyang.

These sorts of challenges may cause some White House political advisers to tell the president to skip South Korea and lead from behind. But if the administration’s heralded rebalance to Asia is to have meaning, Obama must be at the front on diplomacy, trade and security. The U.S. and South Korean governments need the discipline a presidential visit would impose if we are to conclude the unfinished business in our alliance. More important, friends and foes will be watching the president’s words and deeds to see whether the United States really has staying power in Asia. A trip without South Korea would send the wrong signal.