Barack Obama says he “absolutely” has concerns about a Donald Trump presidency, in his first news conference since the US election.
And he advised Mr Trump to change some aspects of his behaviour.
“I think what will happen with the President-elect is that there are going to be certain elements of his temperament that will not serve him well unless he recognises them and corrects them,” he said.
During their face to face meeting on Thursday, he said he offered Mr Trump “honest advice” and highlighted the importance of finding trusted aides for the White House.
“We had a very cordial conversation,” he said. “Do I have concerns? Absolutely.”
Mr Obama told Mr Trump he must reach out to voters who did not support him.
He told journalists he thinks Mr Trump will try to “send some signals of unity” to people who were alienated by what was a ferocious campaign.
And he urged the President-elect “to reach out to minority groups or women or others that were concerned about the tenor of the campaign”.
Mr Obama said the job of President was a big challenge, and the Presidency was bigger than one person.
But he promised that he and his team will do all they can to help make the transition peaceful and smooth.
Mr Trump needed to be given the “rope and space” for a “reset”, he said, reflecting on his own arrival in the White House during the economic crisis.
He said Mr Trump will have more “time and space” than he had to make “judicious decisions”.
Mr Obama said that immigration was good for the American economy if it was orderly and lawful, and he would urge Mr Trump to think “long and hard” before he cracks down on young undocumented immigrants.
He refused to comment about Mr Trump’s first senior appointments, including naming Stephen Bannon as the chief strategist of his administration.
Following Hillary Clinton’s defeat, Mr Obama said Democrats must accept the result, compete everywhere and show up everywhere.
He is about to leave for his last foreign trip, a week-long tour to Greece, Germany and Peru.
Mr Obama said he would be reassuring America’s allies that Mr Trump supports NATO, despite comments made during the campaign that he wanted other countries to pay more towards it.