A Hillary Clinton campaign staffer lost his cool Sunday after Donald Trump said that Army Capt. Humayun Khan would still be alive had he been president when Khan was fighting in Iraq.

Jesse Lehrich, Clinton’s foreign policy spokesman, tweeted, “Hey, @realDonaldTrump -- regarding your claim that Captain Khan would be alive if you were president: go f--- yourself. #debate.”

Minutes later Lehrich acknowledged making a mistake. “I want to apologize for the clearly inappropriate nature and language of this personal tweet. Sorry all,” he tweeted.

Trump said in his presidential debate with Hillary Clinton, the Democratic presidential nominee, that Khan “would have been alive today,” if he had been president when the officer was killed in Iraq in 2004 -- in response to Clinton revisiting Trump's criticism of Khan's family this summer.

Trump, the Republican nominee, on Sunday also called Khan an American hero.

The officer’s father, Khizr Khan, a Muslim-American and Harvard- educated attorney, said onstage at this summer’s Democratic National Convention that Trump was unpatriotic for his views of Muslims and his plans to ban them from entering the United States.

Trump later questioned why Khan’s wife, Ghazala Khan, stood silently while her husband spoke, which resulted in sharp criticism of Trump.