Peter Alexander of NBC News, during a news conference, accused Trump of misquoting his victory margin as the largest since Ronald Reagan.
Opinion polls show that many voters are backing Clinton primarily to stop Trump from getting into the White House. If they believe he has no hope of winning, what would their motivation be to turn up at the polls?
Hillary Clinton and Donald Trump sought to burnish their foreign-policy credentials on Monday by meeting world leaders at the UN.
Clinton clinched the nomination with the added support of superdelegates, party leaders who are free to back any candidate.
The campaign of Bernie Sanders has vowed to keep up the fight, saying it was wrong to count the votes of superdelegates before they actually cast ballots at the Democratic National Convention in July.