Story highlights "@HillaryClinton was angry + defensive the entire time," Priebus tweeted

Clinton campaign response: "That's just what taking the office of President seriously looks like"

Washington (CNN) Republican National Committee Chairman Reince Priebus slammed Hillary Clinton Wednesday for seeming angry and not smiling more during a national security forum.

"@HillaryClinton was angry + defensive the entire time - no smile and uncomfortable - upset that she was caught wrongly sending our secrets," he said in a tweet about the "Commander in Chief" forum hosted by NBC.

@HillaryClinton was angry + defensive the entire time - no smile and uncomfortable - upset that she was caught wrongly sending our secrets. — Reince Priebus (@Reince) September 8, 2016

His tweet was swiftly criticized on social media for being sexist.

The Clinton campaign quickly responded to his tweet: "Actually, that's just what taking the office of President seriously looks like."

Actually, that's just what taking the office of President seriously looks like. https://t.co/Pyn92mesom — Hillary Clinton (@HillaryClinton) September 8, 2016

And her communications director, Jennifer Palmieri, who previously served at the White House, tweeted: "People. Reince actually said HRC needed to smile more. This is real."

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