The United States cannot play an active role on the global stage without the resources and political will to do so, but both are in increasingly short supply these days, said a visiting North-east Asia expert yesterday .

This trend, however, seems unlikely to be reversed because of political forces in the US, said Dr Richard Bush of the Brookings Institution think-tank.

President Donald Trump, who ignited a new round in a longstanding debate on the wisdom of US activism, is merely a symptom of deeper political trends, he added.

A former Washington official and de facto US representative to Taiwan, Dr Bush argued that America's diminishing appetite for global leadership paves the way for China to seize the initiative in shaping the global economic frameworks.

He set out his case for this prognosis in a public lecture organised by the S. Rajaratnam School of International Studies, a year and a day since Mr Trump was elected president.

It was attended by about 50 students, academics and diplomats.

Dr Bush, pointing to Mr Trump's current tour of Asia, noted that he and Chinese President Xi Jinping talked about the great potential for cooperation. "I hope that is the reality going forward... but recent experience has shown competition is more likely than cooperation. Our friends and allies will make their own decisions about what it means for their interests," he said.

Dr Bush traced America's relative reluctance to be involved in global affairs to its unresolved political debate over how to use its resources.

The main options were: on government, on social welfare such as pensions and healthcare, on defence or to reduce taxation.

The President's Republican Party favours cutting taxes and put forward a tax reform plan last week.

Said Dr Bush: "Even if Trump goes back to mainstream thinking on US global activism, he cannot carry out that strategy without resources."

He added: "How much we spend on diplomacy and defence will define how much we play a role on the global stage.

"If our capabilities in East Asia are declining and if our leaders back home are not able to address the problems of our society, then the region will get the message."

Amid the shifting relationship between China and the US, Asean remains very important, Dr Bush said in response to a question on how the regional grouping should raise its profile. Mr Trump recently addressed the idea of an Indo-Pacific region, and "if one is going to think in terms of the Indo-Pacific, then Asean is right in the centre of a large and diverse set of countries".

He urged the 10 Asean countries to "be frank" with America about their individual interests, and those of the group. The reason is that it helps for America to hear about "the ways in which US policy may be acting in ignorance of those interests or contrary to them", he added.

Dr Bush cited how in the Obama administration's later years, it was important for America to know that Asean countries were worried about US failure to respond to China's efforts to build islands in the South China Sea. In 2015 and 2016, then President Barack Obama drew a line in the sand on multiple occasions on land reclamation by China in the disputed waters.

"Without that emphasis, and without those criticisms, we might not have done what was probably necessary to do," said Dr Bush, adding: "Asean does have a message on certain issues and may have important policy contributions to make."