President Barack Obama is following up his endorsement of Hillary Clinton by scheduling a joint appearance with the presumptive Democratic presidential nominee next week in Charlotte, North Carolina, and escalating his attacks on Republican candidate Donald Trump.

Speaking at a news conference Wednesday during an international meeting in Ottawa, Ontario, Obama said Trump promotes "nativism or xenophobia or worse." Obama said, "I'm not prepared to concede the notion that some of the rhetoric that's been popping up is populist." He argued that being a populist means caring about workers, children and the poor, and he said Trump is someone "who has never shown any regard for workers, who has never fought on behalf of any social justice issues," and who has opposed programs to expand economic opportunity.

Obama had originally planned the pro-Clinton event for June 14 in Green Bay, Wisconsin, but postponed it because he was dealing with a mass shooting in Orlando, Florida, which occurred June 12.

Clinton strategists say the choice of North Carolina signals that Clinton believes she can win the state in November and will intensify her campaign there.

Democratic strategists say this will be the first of many Obama appearances for Clinton, and there is increasing evidence that he can make a difference. Obama's approval ratings have improved, which may make some voters more interested in supporting Clinton in the general election as Obama's political heir. A recent CBS News/New York Times poll finds that 50 percent of Americans approve of the job Obama is doing while 43 percent disapprove. A year ago, only 42 percent approved and 48 percent disapproved. Other polls show similar results. Gallup gives Obama an approval rating of 52 percent while disapproval is at 44 percent. A recent NBC News/Wall Street Journal poll gives Obama 51 percent approval and 46 percent disapproval.