Obama's assessment of the GOP standard-bearer, in response to a question at a news conference, comes as the president has become more forceful in his criticism and increasingly willing to wade into the 2016 election cycle. The president also questioned Trump's readiness for office during a commencement address at Rutgers University this month, although he did not mention the business mogul by name.
Yet Obama remained cautious about weighing in on the Democratic contest between former secretary of state Hillary Clinton and Sen. Bernie Sanders of Vermont, whose primary fight has become increasingly personal in recent weeks. Some Democrats have begun to urge Sanders to drop his campaign, with Clinton's steady lead in delegates and despite the senator's wins in primaries and caucuses.
"During primaries, people get a little grumpy with each other," Obama said. "That's the nature of the process. You start off thinking this is fine, a friendly competition in which we'll debate ideas. Then someone says something or another."
The president added that he has "urged both sides to try to stick to the issues because a lot of grumpiness arises when folks feel they are not talking about the issue but talking about personalities and character."
Of the Democratic contenders, Obama said: "They're both good people. I know them both well. I think that it’s important for us to try to end this in a way that leaves both sides feeling proud of what they've done. Both sides have run serious and competitive races. ... I'm proud of Democrats for doing that."
Obama was asked whether the drawn-out Democratic primary would make it more difficult for the party to turn its attention to Trump for the general election campaign.
"No," he replied. But he acknowledged that "it would it be nice if everybody was immediately unified and singing 'Kumbaya' about whoever was the nominee and it could end up being two weeks of vacation and recharging, absolutely. I guarantee you the eventual nominee wishes it was over now. This is a grind. It's hard."