Former US President Barack Obama decided to put a break on his extended vacations and reappeared in public Monday saying he is ready to take up the challenge of encouraging young people to take part in politics, while making no mention of his successor, Donald Trump, who is approaching the 100-day mark of his presidency.

Speaking at the University of Chicago, in his adopted hometown, the former US president, looking relaxed after an extended vacation time to write his memoirs, opened to the event by quipping: "So, uh, what's been going on while I've been gone?" that made the audience laugh.

The remark was Obama's most direct reference to the big changes that have taken place in Washington since he handed over the Oval Office to Trump last Jan. 20.

Two days before leaving power, Obama promised he would speak up if Trump's actions threatened the nation's key values, something that up to now he has only done through a spokesperson to criticize Trump for his anti-Muslim immigration order that was suspended by a judge.

Obama expressed his intention not to criticize Trump in the public and private appearances he has scheduled for the coming months, since he wants to do nothing that will increase the country's rising political tensions, his advisers told The New York Times last week.

The former president is instead concentrating on his "next job" after the presidency, which he said will largely consist of trying to influence political life in the United States, something he considers damaged by low voter turnouts for elections, the excessive influence of special interests and growing party extremism.

"The single most important thing I can do is to help in any way I can to prepare the next generation of leadership to take up the baton and to take their own crack at changing the world," Obama said Monday.

Through the Obama Foundation and his future presidential library, both in Chicago, the former president hopes to discover young people with talent and passion for community work and give them the tools they need to do it successfully.

His talk in Chicago was the first in a series of public events that will include a ceremony in Berlin next May with German Chancellor Angela Merkel.

The Democratic politician recalled that the United States has "the lowest voting rates of any democracy, and low participation rates then translate into a further gap between who is governing us and what we believe."

"The only folks who are going to be able to solve that problem are going to be young people," Obama said. "So the question then becomes: What are the ways we can create pathways for them to take leadership - for them to get involved?" 

Obama, who had expected Hillary Clinton to succeed him, has kept a low profile since the end of his second term. He has focused on building his foundation and starting to write his memoir, along with taking some holiday time in Palm Springs, California and the British Virgin Islands, where he spent time with billionaire businessman Richard Branson, and on the yacht of music mogul David Geffen near the island of Moorea in French Polynesia. But he issued a statement in support of protests against Trump’s travel bans on several Muslim-majority countries.

On Monday, after brief remarks, the 44th president moderated a panel discussion with young activists and leaders. He hit on themes familiar from his presidency and his earlier career as a community organiser in Chicago. There was also self-deprecation – “I’m old” – and lighthearted advice about the diplomacy of marriage and not oversharing on social media. “If you had pictures of everything I’d done in high school, I probably wouldn’t have been president of the United States,” he said, as reported in The Guardian.