"I think the Republican nominee is unfit to serve as president," Obama said at a White House news conference. "I said so last week. He keeps proving it."
Obama added that Trump has shown he is "woefully unprepared to do this job" after his comments on military families as well as his handle on foreign affairs.
He slammed Trump for his rhetoric, including the one against parents of a slain Muslim-American soldier and said the Republican presidential nominee doesn't have the judgment, temperament or understanding to be the president of the country.
"There has to come a point at which you say enough," Obama said.
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"The notion that he would attack a Gold Star family that made such extraordinary sacrifices on behalf of our country, the fact that he doesn't appear to have basic knowledge around critical issues in Europe, in the Middle East, in Asia, means that he is woefully unprepared to do this job," the president said at the White House.
Obama remarked that Republican denunciations of Trump "ring hollow" as they continue to endorse Trump.
"This isn't a situation where you have an episodic gaffe. This is daily and weekly where they are distancing themselves form statements he's making."
Obama said this opinion of Trump is shared by prominent Republicans.
"I think what's been interesting is the repeated denunciations of his statements by leading Republicans, including the speaker of the House and the Senate majority leader and prominent Republicans like John McCain," he said.
"The fact that it has not yet happened makes some of these denunciations ring hollow. I don't doubt their sincerity. I don't doubt that they were outraged about some of the statements that Mr Trump and his supporters made about the Khan family," he said referring to the statements made by Trump against the parents of Muslim-American soldier Humayun Khan who was killed in Iraq war by a suicide bomber.