Sen. Tim Kaine on Thursday went after President-elect Trump's national security adviser for sharing fake news stories that "most fourth graders" wouldn't believe.

Last year, retired Lt. Gen. Michael Flynn tweeted out a fake news story that accused Hillary Clinton of being involved in sex crimes with children. He later deleted the tweet.

But Kaine, D-Va., said the fact that Flynn shared the story in the first place shows "a sense of gullibility or malice."

"These are stories that most fourth graders would find incredible. That a national security adviser would find them believable enough to share them causes me great concern," Kaine said during a Senate Armed Services Committee hearing on cybersecurity.

The hearing has mostly focused on the Russian hacking of the U.S. presidential election, which included the release of stolen emails from the Democratic National Committee and the spreading of fake news on social media.

Flynn's son also came under fire and was removed from Trump's transition team after spreading a story on social media that Clinton was involved with an illegal sex ring run out of a D.C. pizza shop. The original story prompted a man to show up at the restaurant with a gun to investigate its assertions. No one was hurt.