Donald Trump drew a sharp response from Hillary Clinton's campaign team when he claimed Sunday night that an Army captain killed in Iraq would be alive had he been president.

"Hey, @realDonaldTrump – regarding your claim that Captain Khan would be alive if you were president: go fuck yourself," Jesse Lehrich, Clinton's foreign policy spokesman, tweeted during the second presidential debate.

The forceful rebuke came after a debate that opened with a question from the audience about whether the candidates had modeled "appropriate and positive behavior" for American children.

"I think it is very important for us to make clear to our children that our country really is great because we're good and we are going to respect one another, lift each other up, we are going to be looking for ways to celebrate our diversity and we are going to try to reach out to every boy and girl as well as every adult to bring them in to working on behalf of our country," Clinton replied.

Lehrich apologized in a follow-up tweet. "I want to apologize for the clearly inappropriate nature and language of this personal tweet," he wrote. "Sorry all."

The original tweet is the latest installment in a fight that dates back to the Democratic National Convention. Khan was an army officer of Pakistani descent who was killed during the Iraq war. His parents spoke at the DNC on behalf of Clinton. But Trump invoked him in order to rebut the allegation that he has fanned Islamophobia in the country, after Clinton faulted him for criticizing Khan's parents.

"Captain Khan is an American hero," Trump said. "And 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."

Trump was asked in 2002 if he supported the Iraq invasion. "Yeah, I guess so," he replied. "I wish the first time it was done correctly." By 2004, he was very critical of the war.