False rumors that the Little Rock Nine were paid protesters even forced the NAACP to issue a statement condemning the stories as "pure propaganda." The students were not, in fact, "imported" from the North, said the NAACP's Clarence A. Laws, but rather the children of local residents, including veterans.

When Princeton history professor Kevin M. Kruse pointed out the parallel between Parkland and Little Rock earlier this week, his tweet went viral.

"It's funny," Kruse told The Washington Post on Thursday. "I'm teaching a class right now that does deep dives into three historical moments as a way to teach students how to use documents, and the first one we're doing is on Little Rock. ... So when the 'these students must be paid' thing came up in the news, it took me a day and then I was like, wait a minute, I just read about this."

But the practice of dismissing witnesses to major historical events as mere paid actors goes back much further than the Little Rock Nine.

"It's a theme that crops up throughout civil rights history," said Kruse. "Back then, it was an assumption that African Americans in the South couldn't possibly be upset. They must have been stirred up from the outside, either paid to do this or inspired to do this by propaganda. They couldn't have come up with this on their own.

"I think this is what we see in the Parkland case today," he added. "There's a belief that somehow these 17- or 18-year-olds who witnessed a school shooting ... who saw their friends die, somehow could not have been motivated to respond to that on their own, that they would need some sort of outside direction for that protest to take shape."

The crisis actor slur dates back to shortly after the Civil War, when former slaves who testified before Congress were slandered by Southern politicians as stooges paid to lie about their experiences, according to Boston College history professor Heather Cox Richardson.