President Obama says he hopes the Democrats “pull things together” after Hillary Clinton became the party’s presumptive nominee for president.
Her rival, Bernie Sanders, has vowed to fight on despite pressure to step down from party figures.
Mr. Obama stopped short of calling for Mr. Sanders to drop out, instead saying the Vermont senator had made Mrs. Clinton a “better candidate”.
The two men are due to meet at the White House later on Thursday.
Afterwards, President Obama is tipped to formally endorse Mrs. Clinton and call for the party to unite against the presumptive Republican nominee, Donald Trump.
Speaking on NBC’s Tonight Show, Mr. Obama admitted the race had been “ouchy”.
But he went on to say this was welcome: “It was a healthy thing for the Democratic Party to have a contested primary.
“I thought that Bernie Sanders brought enormous energy and new ideas. And he pushed the party and challenged them. I thought it made Hillary a better candidate.”
He added: “My hope is, is that over the next couple of weeks, we’re able to pull things together.”
Mrs. Clinton won four out of six primaries on Tuesday, giving Mr. Sanders virtually no path to the nomination.
Despite this, he said he planned to “fight for every vote” in the next primary – the last before the nomination convention next month.
Mr. Trump has pitched to Mr. Sanders’ supporters: “Bernie Sanders must really dislike Crooked Hillary after the way she played him. Many of his supporters, because of trade, will come to me.”
But Mr. Sanders said his campaign would not support Mr. Trump, “a candidate whose major theme is bigotry”.
During his interview, Mr. Obama said he was “worried” for the Republicans, saying the US needed a “healthy two-party system”.
“The main role I`m gonna be playing in this process is to remind the American people that this is a serious job,” he said.
“You know, this is not reality TV. I’ve seen the decisions that have to be made. And the work that has to be done,” he added, in a clear barb aimed at Mr. Trump, a former star of TV series the Apprentice.