Speaking at a press conference in Japan, Obama said that international leaders were surprised and concerned about an all-but-certain Trump nomination, and they have good reason to be.
"They are not sure how seriously to take some of his pronouncements but they're rattled by him—and for good reason, because a lot of the proposals that he's made display either ignorance of world affairs or a cavalier attitude," Obama said.
Obama also took Trump to task for seeming to care more about his online personality than about unity and making the country safe.
"(Trump shows) an interest in getting tweets and headlines instead of actually thinking through what actually is required to keep America safe and secure and prosperous and what's required to keep the world on an even keel," he said.
Trump has strained relations with some world leaders already. He's engaged in a war of words over a border wall with former Mexican President Vincente Fox. He's said he and British Prime Minister David Cameron, who called him "stupid and wrong," would not get along and sparred with the newly-elected Muslim mayor of London over his proposed ban on Muslim immigration.
Obama also weighed in on the Democratic presidential race during the press conference, maintaining that the party would unify despite the tone of the race.
"During primaries, people get a little grumpy with each other. You know, it's just the nature of the process," he said. "Somebody says one thing. Another person says another thing. That result is a little sharper than I expected. Somebody's supporter pops off. There's a certain build up of aggravation."
Watch below via NBC News: