Khizr Khan, 66, father of Army Capt. Humayun Khan, had stunned a national audience in July with a speech during the Democratic National Convention directly confronting the controversial real estate tycoon, saying Trump "has sacrificed nothing and no one".
Khan had stunned a national audience with his moving tribute to his son at the Convention in Philadelphia while posthumously receiving a Bronze Star and a Purple Heart after he was killed by a suicide bomber in Iraq in 2004.
Although this is Khan's first time on the campaign trail for Clinton, he appeared in an emotional television advertisement to support her candidacy last week, asking Trump whether his son would "have a place in your America?"
Trump, who is known for making controversial statements including a call for banning Muslims entering the US, had hit out at Khan following his July remarks and had questioned whether Khan's wife was even "allowed" to speak. His comments, however, drew sharp criticism from different quarters, including from his own party, both for attacking a mourning mother and because many considered them racist and anti-Muslim.