“Xi Jinping’s ambitions are dangerous for the whole world,” General Cuong said. “China uses its money to buy off many leaders, but none of the countries that are its close allies, like North Korea, Pakistan or Cambodia, have done well. Countries that are close to America have done much better. We must ask: Why is this?”
As with other Southeast Asian nations acutely aware that they are positioned in China’s backyard, Vietnam is worried about American inattention.
In the name of halting Communism, the United States once sent troops to Indochina and propped up dictators elsewhere in Asia. But the American-devised security landscape also created a stable environment in which regional economies expanded.
Now, Mr. Trump’s decision to take the United States out of the Trans-Pacific Partnership trade pact, which would have given 11 other economies an alternative to a Chinese-led economic order, has left the Vietnamese feeling vulnerable.
“As Vietnamese, we are always trying to find a way to balance China’s power,” said Nguyen Ngoc Anh, a professor at the Foreign Trade University in Hanoi. “For us, TPP isn’t just an economic issue. It’s also about geopolitics and social issues.”
Ms. Anh noted that local liberals had cheered the trade pact because it would have forced Vietnam to adhere to international labor and government accountability standards that Hanoi might otherwise not meet.
With the 11 other members of the pact agreeing to proceed without the United States, Washington’s withdrawal — not to mention Mr. Trump’s “America First” speech at the APEC meeting on Friday — leaves some nations wondering if their best option may be Chinese-backed trade pacts and financing deals that have fewer guarantees for workers and less official transparency.
“We are both Communist countries, but people like me in Vietnam don’t want to develop the same way that China has,” said Ms. Anh, who studied economics in Soviet-era Czechoslovakia. “We want to follow the Western-oriented way.”
While the United States is the largest market for Vietnamese exports, Vietnam’s biggest trading partner is China. Yet Vietnam runs a significant trade deficit with its populous neighbor, and Vietnamese economists worry that China doesn’t play fairly.
“China is one of the few countries in the world that doesn’t observe international law in many areas,” said Le Dang Doanh, an influential economist who has advised members of the Vietnamese Politburo on trade.
The Vietnamese watched in alarm last year when Beijing reacted to an international tribunal’s dismissal of China’s expansive claims over the South China Sea by ignoring — and even mocking — the judgment. Vietnam and four other governments have claims of their own on the resource-rich waterway that conflict with China’s.
It is hard to overstate the level of Vietnamese antipathy toward China. In a country where public protest is rare and risky, some of the few large-scale demonstrations in Vietnam in recent years have been against the Chinese.
But this national aversion puts Vietnam’s leadership in a bind. It cannot ignore China’s growing economic magnetism. For many members of APEC, China now ranks as their No. 1 trading partner.
In return for investment and project financing — roads, railways, dams, airports and colossal government buildings — leaders of regional economies are increasingly doing Beijing’s bidding.
Cambodia and Laos have given crucial support for Beijing’s South China Sea claims. Thailand has complied with Beijing’s demand that it return Chinese dissidents who once counted on it as a haven.
Even the Philippines has appeared to yield, despite the fact it lodged the successful South China Sea suit at The Hague. Days before Mr. Trump’s visit to Manila this Sunday, it disclosed that President Rodrigo Duterte had ordered construction halted on a disputed sandbar in the South China Sea, a move widely regarded as intended to placate Beijing.
Since taking office last year, Mr. Duterte has deemed the era of American military and economic pre-eminence over, and has called China his country’s best and faithful friend. He has been rewarded with billions of dollars in infrastructure investment from Beijing.
“The U.S. has been playing catch-up to China’s charm offensive since the turn of the new century,” said Tang Siew Mun, who heads the Southeast Asia center at the Iseas-Yusof Ishak Institute, a think tank in Singapore.
Vietnam, more than any other country, has grown practiced at divining when not to challenge the two Pacific powers — both of which it fought within the last half-century.
In the 1970s and 1980s, China seized spits of land in the South China Sea that Vietnam had controlled or that were unoccupied but claimed by Hanoi.
Yet perhaps sensing an American reluctance to confront China in the South China Sea, Vietnam has declined to take China to international court, as the Philippines did, even as the Chinese have turned disputed reefs and sandbars into militarized islands.
Chinese pressure continues, despite the United States’ supplying the Vietnamese Coast Guard with a cutter and new patrol boats.
This year, a Spanish company with prospecting rights from Vietnam suspended drilling in an oil block off the coast of Vietnam. Beijing claims part of the waters as its own.
In 2014, the Chinese parked a state-owned oil rig off Danang, where Mr. Trump attended the APEC summit meeting on Friday, in a forceful incursion into what Hanoi considers its territorial waters.
“Living next to China, which has ambitions to become the most powerful country in the world, is not easy,” said Vo Van Tao, a popular political blogger. “To lower the heat, Vietnam needs to withdraw from areas that belong to Vietnam.”
Grand strategy is beyond the worldview of Vietnamese like Do Van Duc. In 1979, he was stationed on the border with China, as part of an antiaircraft artillery unit, when hundreds of thousands of People’s Liberation Army soldiers from China flooded south.
The Vietnamese, while outmanned, put up an unexpectedly robust defense. Within a month, the Chinese, professing that they had taught the Vietnamese a lesson for interfering in regional geopolitics, withdrew.
During the war with China, Mr. Duc was only 17 years old, but he came to understand one thing then that today, as a security guard living in Hanoi, he said he still clings to.
“We cannot trust the Chinese,” he said. “They are our ancient enemy, and that will not change.”