SINGAPORE - To Mr Barack Obama, who crafted the essential rules for winning elections in the digital age, the buck is back with the voter.

Or, as the man who collected the highest number of votes ever cast for a White House candidate in his improbable bid to become America's first black president put it: the world today faces not just a crisis of leadership but a crisis of citizenship.

Mr Obama retired three years ago after holding office for eight years and remains a highly feted and inspirational figure across the globe.

His pronouncements on whether leaders are letting the world down came during a talk on Monday (Dec 16), the last day of his four-day trip to Singapore during which he also attended a charity event and called on Prime Minister Lee Hsien Loong.

Asked by the moderator of an hour-long conversation if today's global leadership should be a source of worry, Mr Obama made no mention of his successor Donald Trump whose winning slogan was a protectionist "America first".

Known for a transactional approach to office, Mr Trump lost little time in overturning key Obama policies - from backing out of what would have been the world's largest free trade pact, the Trans-Pacific Partnership, walking out of Paris accord and the Iran nuclear accord.

Nevertheless, Mr Obama's message was pointed enough and resonated with an audience of business executives packed into a hall in the Singapore Expo on a rainy working day. It was a call to both leaders and their followers to embrace, not shun, the complexity of the ever more interconnected world.

"What we need, in terms of global leadership, is people who are comfortable with and understand complexities," he said, before adding: "But that, of course, requires citizens to be comfortable and understand complexity."

Responding to a question from Mr Nicholas Fang, the Director of Security and Global Affairs at the the Singapore Institute of International Affairs, Mr Obama's argument was lucid. "Part of the challenge we have as humans is that when things get complicated and confusing we tend to want to block it out and look for simple answers," he said.

"So we are, often times, getting a leadership that reflects our own insecurities and problems.

"We are electing somebody whose basic message is that all your problems are a result of that group over there that's not like us.

"We are electing people who say there is no such thing as climate change so that you don't even have to worry about it.

"We elect people who say 'I am the tough guy and if you are worried about crime or terrorists, I'm just going to round everybody up,' which leads to extra-judicial killings or torture or violates human rights.

"That's not just the leader's fault. It's not just a challenge of leadership, it's a challenge of global citizenship."

Instead, he pointed out: "What we should expect our leaders to be doing is to help all of us understand the difficult decisions we have to make... that will bring the people together rather than dividing them."

Mr Obama is credited with reviving an economy wracked with the worst economic crisis since the Great Depression, for bringing the world's biggest polluter in line with global efforts to halt climate change by signing the Paris accord, and for Obamacare - a law that extended healthcare to millions of uninsured Americans.

Asked to name the three things that still keep him awake at night, he listed political polarisation, the unexpected corruption of the social media and climate change.

Blue-collar workers in the developed world were losing jobs and status as a consequence of globalisation, outsourcing and automation, he noted. "There was a backlash, sometimes from the left, more often from the right. And a fall back to tribalism, racism, misogyny, ethnic or sectarian conflicts and strongmen who would come in and exploit some of those divisions."

It was the return, he said, to some of the trends and societal tensions that helped lead to World Wars.

He is considered a past master in the use of the social media, the other source of his anxiety today. "I was an early adapter. I would not have been elected had it not been for our ability to communicate and generate enthusiasm among volunteers and small donors though the social media," he said.

"But what we have seen is an increase in use of that technology to promulgate falsehoods and narratives of hate in the US, Europe, around the world.

"It's not just about how you and I may disagree on the best way to educate our children or organise our economy but now we are disagreeing on - is this a table or a chair or an elephant.

"There is no agreed upon set of facts that we can test our ideas or opinions against. Rather everybody has their own facts. You start seeing political breakdowns as a consequence."

Still, he remains a dealer in hope and change, the two coins of his own presidential campaign.

"I am a cautious optimist who believes there is goodness within us, we have the capacity to reason, there is a natural empathy and a sense of common humanity in us.

"But there is also fear and stupidity and destructive impulses within us. Our job is to get more of the good stuff, to create institutions that encourage more of the good stuff," he said.

For, despite what the headlines say, he noted: "The world has never been wealthier, more educated, less violent, more tolerant. There has never been greater understanding between cultures. But that's not a cause of complacency, there is still suffering everywhere.

"But it should give us some confidence that we can be better."

Mr Obama who admitted to being "annoyed" when he won the Nobel Peace Prize "too early" - just nine months into his first term - sees the average Joe as the solution.

"It's going to take all of us, not just a single leader, not looking for a messiah somewhere, but each of us figuring how do we contribute in our communities to creating better compassion, justice, equity."