Sirota’s hiring as a senior adviser and speechwriter was announced by the Sanders campaign on Tuesday morning after The Atlantic contacted the campaign and inquired about the undisclosed role Sirota held while attacking other Democrats.

Faiz Shakir, Sanders’s campaign manager, confirmed in an interview on Tuesday afternoon that Sirota had been in an advisory role prior to his hiring on March 11. “He was advising beforehand,” Shakir said, explaining that Sirota’s informal work for Sanders goes back months, and was meant to be a trial period to see how the senator, who famously likes to write every word that he says himself, would work with a speechwriter.

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The online fury of Sanders’s supporters was one of the most defining characteristics of his 2016 campaign. Sanders himself has said he is sensitive to that, as well as to accusations that he created divisions within the Democratic Party during his 2016 run against Hillary Clinton. “Negative attacks on Democratic candidates,” Sanders said in 2018, criticizing the Democratic Congressional Campaign Committee for putting out damaging information about an opponent to a favored candidate in a primary, “just continues the process of debasing the Democratic system in this country, and is why so many people are disgusted with politics."

When people have questioned his tactics, Sirota has called them “mentally incapacitated.” Responding in mid-January to those who criticized him online for preemptively railing against the record of O’Rourke, who had not yet entered the race but had been a huge source of concern for Sanders allies since talk of O’Rourke’s potential presidential run picked up last year, Sirota tweeted, “The screaming temper tantrums by Democratic Party operatives whenever reporters scrutinize a lawmaker’s voting record is something to behold. These people quite literally hate democracy.”

At another point, he said his critics “are deranged and/or running a deliberate disinfo campaign.” “Positively unhinged,” he wrote about them a separate time.

Read those comments, Shakir paused. “He used those exact words?” he asked. “I’m sure he regrets the tone.”

None of those comments can be found online anymore. On Monday night, after being contacted for a second time by The Atlantic with a list of specific questions about his undisclosed work for Sanders, Sirota did not respond to the email but deleted more than 20,000 tweets. He left fewer than 200 online.

On Tuesday morning, minutes after his position was announced by the Sanders campaign in a long list of new hires, Sirota said he hadn’t been able to respond to my initial inquiries because he’d been caring for his sick child. He did post a photo on Twitter of himself bowling on Monday evening, wearing a turkey hat.