Ron Nehring, campaign spokesman for Texas Sen. Ted Cruz during the 2016 presidential campaign, said Tuesday that online trolls of unclear origin flooded his Twitter feed whenever he was critical of then-candidate Donald Trump, but not when he attacked other GOP candidates.

“If I had said something critical about Marco Rubio, or John Kasich, or Ben Carson, there was no response on Twitter whatsoever, dead,” Nehring said about his cable news appearances on behalf of Cruz during last year’s campaign. “However, if I was critical of Donald Trump, I would get a torrent of negative comments on Twitter.”

Nehring said when he looked closely at those accounts, they fit into similar parameters: no personally identifiable profile picture, no location listed, and certain buzzwords in the profile description.

“The tone was always extremely hysterical, not something that I would see from typical conservative activists,” said Nehring, a former chairman of the California Republican Party and the Republican Party of San Diego County.

Nehring’s remarks came at a Heritage Foundation event on Russian use of social media to promote disinformation and propaganda. The panelists, experts from Ukraine, Moldova, Latvia and Lithuania, each described their experiences with what they described as Russian efforts to undermine public confidence in their governments, their media and information in general.