In a fiery exchange during Tuesday’s White House press briefing, one reporter pointedly asked Press Secretary Jay Carney how he could be “categorically certain” that no one from the White House was involved in the IRS targeting conservative groups.

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Carney stumbled when asked whether he was basing his claims on assumptions. “I can tell you that … I am not aware of anyone here knowing about it.”

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The reporter continued, “You asserted something categorically and I’m trying to understand how you know that.”

“I am certainly not aware of and am confident that no one here was involved in this,” Carney replied.