President Obama yesterday called Donald Trump "woefully unprepared" and "unfit" to be president:
During a press conference at the White House with Singapore Prime Minister Lee Hsien Loong, Obama posed the question to the Republican Party: "If you are repeatedly having to say what Trump says is unacceptable, why are you still endorsing him?"
"The notion that he would attack a Gold Star family that had 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, the Middle East, Asia means that he is woefully unprepared to do this job," Obama said.
[He] continued that while there have been Republican presidents he has disagreed with, Trump's actions put him in a different category.
"What does this say about your party that this is your standard bearer? This isn't a situation where you have an episodic gaffe," Obama said. "There has to be a point in which you say 'This is not somebody I can support for president of the United States."
That's an extraordinary statement from a sitting president, and may be unprecedented. I know up until the late 19th century it was common for one side to call the other side unfit—just take a look at some of the things Adams and Jefferson said about each other in the election of 1796—but a sitting president? I don't think this has happened since 1920, and even then, Wilson's slams against Cox came during his own party's nominating process.
Also consider that this president, specifically, doesn't usually get into it like that.