The mother of a State Department official who was killed last month in the terrorist attack on the U.S. Consulate in Benghazi, Libya, lashed out at President Obama on Friday for saying in a TV interview that the deaths in the attack were “not optimal.”

Obama was appearing on “The Daily Show” when host Jon Stewart confronted the president about the administration’s shifting explanation for the attack that killed the U.S. ambassador and three other Americans, saying the post-attack confusion wasn’t an “optimal response.”

“Here’s what I’ll say: If four Americans get killed, it’s not optimal, and we’re going to fix it,” Obama said, in an episode that aired Thursday night..

Pat Smith, whose son, foreign service information management officer Sean Smith, was one of those Americans killed in the attack, called Obama’s choice of words “disrespectful.”

“How can you say somebody being killed is not very optimal?” Smith told the Daily Mail. “I don’t think the president has the right idea of the English language.”