Barack Obama has launched his strongest attack yet on Republican nominee Donald Trump, saying he is "unfit" to be president.
He said the businessman was "woefully unprepared" to lead America and "he keeps on proving it".
The president cited Mr Trump's criticism of Muslim parents of a decorated fallen US soldier as evidence the property tycoon should not take over from him in the White House.
He said: "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 of critical issues in Europe, Middle East, Asia, means he is woefully unprepared."
Mr Obama also suggested leaders in the Republican party withdraw their support for the nominee.
"This isn't a situation where you have an episodic gaffe," Mr Obama said of senior figures including House Speaker Paul Ryan and Senator John McCain.
"This is daily and weekly where they are distancing themselves from statements he's making.
"There has to be a point in which you say: 'This is not somebody I can support for president of the United States, even if he purports to be a member of my party'."
'Sacrificed nothing'
At last week's Democratic Convention, Pakistan-born Khizr Khan told the story of his son who was posthumously awarded a Bronze Star and Purple Heart after he was killed in Iraq in 2004.
The parents of Captain Humayun Khan appeared on stage where Mr Khan said Mr Trump "sacrificed nothing and no one" for his country.
Mr Trump then sparked outrage by implying Mr Khan's wife, Ghazala, did not speak while standing alongside her husband because she was forbidden to as a Muslim woman.
Flowers have been left at the grave of Captain Khan at the Arlington national cemetery in Virginia.
Meanwhile, Mr Trump has unleashed his latest verbal attack on his Democratic rival for the White House by branding Hillary Clinton "the devil".
His insult came as he berated Senator Bernie Sanders' decision to endorse Mrs Clinton.
While rallying his supporters in Pennsylvania, Mr Trump said of Mr Sanders: "He made a deal with the devil. She's the devil."
At another rally later, a baby was heard crying and at first Mr Trump said: "I love babies," before saying a few seconds later "Kidding, you can get the baby out of here".
