In other parts of Asia, including the Philippines, Taiwan and Vietnam, Mr. Trump’s willingness to bend to China is fueling worries that the United States will stop trying to counter China’s growing influence in the region.
Washington has been the main critic of China’s efforts to build fortresses atop reefs, rocks and islands in the South China Sea. But the Trump administration, apparently wary of angering Beijing, recently decided to suspend patrols of islands and reefs claimed by China. “The South China Sea is now China’s lake,” said Carlyle A. Thayer, an emeritus professor at the University of New South Wales in Australia.
Mr. Trump’s credibility among Asian allies is now at stake, diplomats and analysts say. He may jeopardize longtime economic and security alliances if he does not show a willingness to look beyond North Korea, they say.
The president also risks pushing countries in the region closer to Beijing if he does not demonstrate that the United States intends to vigorously challenge China’s territorial claims in the sea.
Mr. Trump’s supporters say his unpredictable style and willingness to rethink decades of accepted policy may be an asset, especially in dealing with an intractable leader like Kim Jong-un of North Korea. But his lack of assurances to Asian allies and his efforts to please China have created the appearance that his foreign policy is negotiable.
Secretary of State Rex W. Tillerson, center, with Southeast Asian foreign ministers in Washington last week. He has tried to reassure allies that freedom-of-navigation patrols will continue. Credit Yuri Gripas/Reuters
Antonio T. Carpio, a Supreme Court justice in the Philippines and a critic of China, said he understood Mr. Trump’s focus on North Korea. But he said he worried about the “permanent concessions China may extract from the U.S.”
“Trump’s emerging transactional foreign policy is not reassuring,” he wrote in an email.
South Korea represents one of the more serious rifts that Mr. Trump will confront. Mr. Moon rose to power by vowing a conciliatory approach to North Korea, saying efforts by the United States and others to impose strict sanctions had fallen short. Mr. Trump favors applying maximum pressure on Mr. Kim’s government.
In Taiwan, officials worry that the Trump administration may delay arms sales, including F-35 stealth fighter jets, for fear of inflaming tensions with China. China considers Taiwan part of is territory, and it has repeatedly warned the United States against selling weapons to the island.
Mr. Trump has already shown a willingness to use Taiwan as a bargaining chip with China. Before he took office, he publicly questioned whether the United States should uphold the “One China” policy. But he later backed down, apparently in an effort to curry favor with President Xi Jinping of China.
China has used Mr. Trump’s first few months in office to reinforce its position in the sea, a vast waterway through which over $5 trillion in trade passes each year. China says historical maps show it owns virtually the entire sea, despite overlapping claims by several smaller countries, including Indonesia, the Philippines and Vietnam.
China now has the ability to deploy warplanes and mobile missile launchers on several islands, according to satellite images provided by the Center for Strategic and International Studies in Washington. It has recently put the finishing touches on airport hangars and radar systems.
Mr. Trump’s young administration has sent mixed signals on how it will approach the dispute. During the campaign, Mr. Trump criticized China’s actions in the sea. Secretary of State Rex W. Tillerson has suggested that China should be denied access to the islands it built.
But The New York Times reported last week that top Pentagon officials recently turned down a request for an American warship to sail within 12 nautical miles of Scarborough Shoal, a disputed reef claimed by the Philippines and China.
Mr. Trump has said that the threat posed by North Korea’s missile tests and nuclear weapons development is so grave that it may require temporarily setting aside contentious issues with China, in exchange for Beijing’s exerting more political and economic pressure on Pyongyang.
Aboard the guided-missile cruiser Chancellorsville in the South China Sea last year. The Pentagon recently rejected a request for an American warship to sail near a reef claimed by both the Philippines and China. Credit Bryan Denton for The New York Times
Cheng Xiaohe, an associate professor of international studies at Renmin University in Beijing, said the Trump administration’s decision to halt patrols would send a message that “China’s claims in the sea should be respected and the United States will not challenge that.”
Other countries that claim territory in the sea disagree. Many see it as a patriotic mission to defend territory there against China, and they have grown angry over frequent confrontations with Chinese ships.
Diplomats in the region saw hope in President Barack Obama’s talk of sending more American military and economic resources to Asia. But they were disappointed as China’s building projects continued unabated.
Mr. Trump’s tough talk on China promised a fresh start. Mr. Tillerson went as far as to say during his confirmation hearing that China’s island-building in the South China Sea was “akin to Russia’s taking of Crimea” and pledged to block access to the islands.
But the administration has yet to follow through. And power dynamics are quickly shifting, with the Philippines, once one of America’s strongest allies in the region, publicly distancing itself from the United States and embracing China.
China, on the other hand, has promised to double down on its investment in the region. “China sees a golden opportunity to step into the vacuum of leadership in the region,” said Alexander L. Vuving, a professor at the Daniel K. Inouye Asia-Pacific Center for Security Studies in Honolulu.
Mr. Trump has spoken in recent days with leaders of the Philippines, Singapore and Thailand, inviting each to the White House. Mr. Tillerson has tried to reassure allies that freedom-of-navigation patrols will continue.
Thitinan Pongsudhirak, a professor at Chulalongkorn University in Bangkok, said Mr. Trump seemed to be showing genuine interest in building a strategic network in the region. He said Mr. Trump was wise to de-emphasize human rights concerns with countries like Thailand and the Philippines; otherwise, it would “further push both countries and the rest of the region into China’s orbit.”
“Once the United States regains some weight and credibility in the region,” he added, “then it can rebalance and reconsider U.S. interests and values.”