WASHINGTON (WASHINGTON POST) - Leaders of more than a dozen countries will meet for a major summit in the Philippines in mid-November, but President Donald Trump will not be there. He is planning to skip it and leave the Philippines the day before.

It is a bad signal to send to the region, and it could undermine the overall goal of his Asia tour by calling American regional leadership into question.

At the White House on Monday (Oct 23), Trump said he would "probably" be visiting the Philippines as part of his 12-day trip to Asia early next month.

A National Security Council spokesman told the Washington Post that Trump will be in Manila on Nov 12 and 13 and will meet Philippine President Rodrigo Duterte and others.

But he will not travel the additional 80km to the Filipino city of Angeles on Nov 14 for the East Asia Summit, an annual conference of Asian and world leaders that focuses on the strategic future of the region.

"The President's trip to Asia is extremely lengthy and will be his longest to date - his return to the US on the evening of Nov 13 is entirely schedule-driven," the spokesman said. "You should not read anything into his being absent on the 14th."

The East Asia Summit opens in Angeles on Nov 13, but the major events with world leaders occur on Nov 14.

But the region is sure to read a lot into Trump's absence, according to experts and former officials. By not attending the East Asia Summit his first year in office, even though he will already be nearby, Trump is signalling a lack of interest in the organisation and the project it represents.

"It is a big deal. The Obama administration made a point of investing in these regional institutions in order to demonstrate we are an Asia Pacific power, a resident power in the region. This will only raise more questions about American credibility," said Derek Mitchell, former US ambassador to Myanmar.

"Multilateralism in Asia is often just about showing up, but even that appears to be hard for him."

Multiple administration officials told me there was a lengthy debate inside the Trump administration about the summit, but officials close to Trump were concerned the president did not want to stay in the region for so long and worried he could get cranky, leading to unpredictable or undiplomatic behaviour.

President Barack Obama brought the US into the East Asia Summit after his administration signed the Treaty of Amity and Commerce in South-east Asia in 2009. He became the first American president to attend the summit in 2011 and attended each year thereafter except for 2013, when he cancelled his trip due to the US government shutdown.

Mitchell said the hosts scheduled the summit close to other regional events, including the Asia-Pacific Economic Cooperation (Apec) meetings, specifically to accommodate the US president.

Trump will attend Apec meetings in Vietnam on Nov 10.

"They tend to schedule (the EAS) to make it easier for the United States to attend," he said. "It's not necessarily convenient for others. I'm sure it's frustrating to many of our partners."

Secretary of State Rex Tillerson may stay in the Philippines for the East Asia Summit, but it's not the same, said Ernest Bower, senior adviser for South-east Asia Programme at the Centre for Strategic and International Studies.

"Tillerson can sit in the president's seat, but the symbolism of that will be the headline of the day," he said.

The East Asia Summit is unique because it focuses on greater strategic issues, as opposed to the economic focus of Apec, said Bower. Trump's absence is part of a pattern of his administration downgrading the importance of multilateral organisations and forums overall.

The East Asia Summit includes the 10 nations of the Association of South-east Asian Nations plus Russia, China, Australia, New Zealand, Japan, India and South Korea, along with the US.

It is a missed opportunity for Trump to show all those countries that the US is still committed to the strengthening regional integration and cooperation as China becomes more aggressive and expansionist, said Bower.

"The rest of Asia needs us to be there," Bower said. "Since you've flown all that way, I can't imagine not staying for that last 24 hours just to keep America in the game. It's shocking."

Not all Asia experts think Trump skipping the East Asia Summit is such a disaster. After all, Trump will spend 12 days on his Asia trip and visit several countries including Japan, South Korea and China.

That should reassure the region of Trump and America's commitment, said Dan Blumenthal, director of Asian studies at the American Enterprise Institute.

"I don't think it's that big of a deal," he said. "What's a bigger deal is what comes out of the actual Duterte meeting and other bilaterals, the fact that he's out there for so long and meeting so many leaders and the content of the policy."

Big deal or not, it's an unforced error that will cause concern among allies and celebration by adversaries.

Trump should just stay one extra day in the country he's already going to, to make sure his Asia trip does not end in doubts about whether the US is really showing up in the region.