In response to US actions, seven out of the ten ASEAN member states also downgraded their representation, sending their foreign ministers instead.
A US diplomat has voiced Washington's "extreme" concern over the move by the majority of ASEAN's leaders not to personally attend the special event, calling it an “intentional effort to embarrass” Trump.
“We are extremely concerned by the apparent decision", the diplomat was quoted by Kyodo News as saying.
So could Trump’s absence from the Bangkok summits be a sign of rising US disinterest in the region? Many experts believe this is the case.
“Trump sending someone less than the alternate Head of State (the vice president) to a meeting with ASEAN heads of state in an important annual event tends to reinforce their perceptions that Southeast Asia is not really a priority for the US", says Dr Jay Batongbacal, director of the University of the Philippines Institute for Maritime Affairs and Law of the Sea.
While Dr Batongbacal noted that the US president might be too preoccupied with an ongoing impeachment inquiry against him, he didn’t have a valid excuse not to attend or at least send an appropriate representative.
Dr Le Hong Hiep, a fellow at the Institute of Southeast Asian Studies in Singapore, for his part, explained that despite Trump missing this year's gathering the US President has invited ASEAN leaders to a special summit in the United States in early 2020.
But, nevertheless, he believes that Trump’s absence should not be exaggerated and should be put into context.
“From what I see, the US remains engaged with the region and Trump’s absence from the summit does not mean Washington has changed its policy direction", Dr Le Hong Hiep added.
Singapore, Malaysia, Indonesia, Brunei, Cambodia, Myanmar, and the Philippines only sent only their foreign ministers to the ASEAN-US Summit, and only the leaders of Thailand, Vietnam, and Laos attended the meeting.
“I don’t think ASEAN leaders intended to “embarrass” Trump. Rather, it could be their efforts to pressure the US to maintain its engagement with the region", director of the Centre for Asian Pacific Studies at Lingnan University in Hong Kong, Dr Zhang Baohui said.
The countries in the region want the US to maintain its presence, especially amid China’s increasing role, according to Dr Baohui. But Trump’s decision to skip the summit for the second year straight has raised concerns among East Asian nations with many fearing rising US disinterest in the region.
“My guess is that they thus use the boycott to show disappointment with the Trump administration’s policy in the region", the scholar added.
Trump’s special envoy Robert O'Brien delivered a message from the president at the summit reaffirming the United States’ commitment to a strategic partnership with ASEAN and its support of the organisation's central role in the Indo-Pacific region.
But, John Short, a political analyst and professor of Public Policy at the University of Maryland, says that Trump has shown little interest in the region, and the fact that the Trump administration didn't even send a member of the cabinet to the EAS and US-ASEAN summit only proves it.
“ASEAN looks to a US presence in the region to counter China's growing influence and especially Chinese claims in the South China Seas that impinge on the maritime claims of at least 5 ASEAN countries", Mr Short said.
But despite the latest snub by the US president, it is important for both US and ASEAN states to maintain a strong relationship as they have a “shared long-term objective of providing a counterweight to Chinese power in the region", the political analyst concluded.
*ASEAN - Association of Southeast Asian Nations