Democratic presidential hopeful Vermont Senator Bernie Sanders speaks during the ninth Democratic primary debate of the 2020 presidential campaign season co-hosted by NBC News, MSNBC, Noticias Telemundo and The Nevada Independent at the Paris Theater in Las Vegas, Nevada, on February 19, 2020.

Twitter did little to lend credence to Democratic presidential hopeful Bernie Sanders' suggestion at the Las Vegas Democratic debate that outside actors could be responsible for abrasive attacks by people claiming to be his supporters online.

At Wednesday's debate, the senator from Vermont defended the "99.9%" of his supporters on Twitter that "are decent human beings," after moderators asked whether his supporters are "making it harder for Democrats to unify in November."

"And if there are a few people who make ugly remarks, who attack trade union leaders, I disown those people. They are not part of our movement," he said.

Sanders later raised the possibility that foreign trolls could be responsible for some of the negativity among his supporters, alluding to the misinformation campaign launched by Russian actors in the lead-up to the 2016 election.

"All of us remember 2016, and what we remember is efforts by Russians and others to try to interfere in our election and divide us up. I'm not saying that's happening, but it would not shock me," Sanders said.

Twitter said if it had evidence of such activity, it would be disclosed.

In a statement to CNBC, a spokesperson said, "Using technology and human review in concert, we proactively monitor Twitter to identify attempts at platform manipulation and mitigate them. As is standard, if we have reasonable evidence of state-backed information operations, we'll disclose them following our thorough investigation to our public archive — the largest of its kind in the industry."

A Facebook spokesperson also told CNBC earlier this week that the company has no evidence that Russians are manipulating activity from Sanders' supporters online.

A spokesperson for Sanders' campaign was not immediately available to comment.

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