Donald Trump Stands by Claim Capt. Khan Would Be Alive if He Had Been President "We wouldn't have been in this horrible, horrible mistake," Trump said.

 -- Republican presidential nominee Donald Trump doubled down on his assertion that slain U.S. Army Capt. Humayun Khan, a Muslim soldier who died in Iraq in 2004, “would be alive today” if Trump had been in the White House.

“Had I been president, Captain Khan would be alive today. We wouldn't have been in this horrible, horrible mistake, the war in Iraq,” Trump said in an exclusive interview with ABC News’ George Stephanopoulos.

Khan’s story became a part of the campaign after his father, Khizr Khan, criticized Trump as a man who had “sacrificed nothing and no one” during the Democratic National Convention this summer. Trump responded by questioning whether Ghazala Khan, who appeared with her husband on stage, was “allowed” to speak.

During the second presidential debate earlier this month, Clinton accused Trump of never apologizing to anyone, specifically the Khan family.

“First of all, Captain Khan is an American hero,” Trump responded at the debate earlier this month in St. Louis. “If I were president at that time, he would be alive today, because unlike her, who voted for the war without knowing what she was doing, I would not have had our people in Iraq.”

Asked by Stephanopoulos whether he should apologize for his comments after Khan's speech at the DNC, Trump declined to say, but noted he has “great respect” for the family.

“I have great respect for, I mean, the son is a great hero,” the Republican nominee said.

Democratic presidential nominee Hillary Clinton hit Trump for his comments to Stephanopoulos at a joint campaign rally with First Lady Michelle Obama in North Carolina today.

“Military families have come up against a lot in this election. It just made me boil when Donald Trump disrespected a Gold Star family, Mr. And Mrs. Khan. He hasn't apologized to them, he made it worse," she said. "Just yesterday he said again that if America had only made him president years ago their son, Captain Khan, would still be alive. Honestly, I don’t understand how anyone would want to rub salt in the wounds of a grieving family.”

Khizr Khan hit the campaign trail for the first time yesterday in support of Clinton, meeting with community leaders, volunteers, veterans and military families in Norfolk, Virginia.

"This is the most cruel thing you can say to grieving parents, that if I was there this would not have happened,” Khan told ABC News yesterday in response to Trump's comments. “There's no sincerity in those remarks…This is one character that a leader must have to be the leader of a great country, to be the commander-in-chief of the Armed Forces of the United States: empathy. And this person totally lacks that.”

Trump reiterated that he has been against the war in Iraq from the beginning, despite a tape of the real estate mogul’s appearance on Howard Stern’s show in 2002 when the radio host asking Trump whether he was “for invading Iraq.” Trump responded, “Yeah, I guess so.”

Trump explained the apparent contradiction.

“That was the first time I was ever even asked about Iraq,” Trump told Stephanopoulos yesterday. “That was long -- that was way before. If you look at just before the war started, I said, ‘Don't do it. It's a mistake. You're going to destabilize the Middle East.’"