Story highlights Donald Trump attacked Hillary Clinton after the FBI released notes from its interview with her

Trump also hit Clinton over tightening polls, and highlighted revelations from the FBI's report on its investigation

(CNN) Donald Trump criticized Hillary Clinton on Sunday for not knowing what the "(C)" label meant when it was used on her State Department emails.

But the Republican presidential nominee apparently doesn't know what it means either.

"Lyin' Hillary Clinton told the FBI that she did not know the 'C' marking on documents stood for classified. How can this be happening?" Trump wrote on Twitter.

Lyin' Hillary Clinton told the FBI that she did not know the "C" markings on documents stood for CLASSIFIED. How can this be happening? — Donald J. Trump (@realDonaldTrump) September 4, 2016

John Noonan, a national security adviser to Jeb Bush and Mitt Romney, observed that Trump had incorrectly ascribed "classified" to the "C" markings -- they actually denote a lower security status, "confidential."

Noonan wrote, "(C) stands for CONFIDENTIAL. Confidential, Secret, Top Secret are levels of classification. DoD Directive 5200.01."

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