U.S. President Donald Trump's lengthy Asia trip is winding down as it began, with a visit meant to be centred on trade and North Korea shadowed by questions about Russia.

Trump was in the Philippines on Monday and remains dogged by things he has said, and has not said, about Russia.

On Saturday, he dismissed the former U.S. intelligence officials who said Russia meddled in the 2016 presidential elections as "political hacks."

On Sunday, he tried to have it both ways, saying he believes both the U.S. intelligence agencies when they say Russia meddled and Russian President Vladimir Putin's sincerity in claiming that his country did not.

Former CIA director John Brennan said Sunday on CNN's State of the Union that Trump is trying to "delegitimize" the intelligence community's assessment.

'Short and fat'

Earlier, Trump had exchanged schoolyard taunts with the country's leader Kim Jong-un. "Why would Kim Jong-un insult me by calling me 'old,' when I would NEVER call him 'short and fat?'" Trump tweeted from Vietnam, adding: "Oh well, I try so hard to be his friend — and maybe someday that will happen!"

Asked whether he could really be friends with Kim, Trump said, "I think anything's a possibility. Strange things happen in life."

Trump and Putin did not have a formal meeting while they were in Vietnam for the Asia-Pacific Economic Cooperation summit, but the two spoke informally several times and reached an agreement on a number of principles for the future of war-torn Syria.