David Sirota, a journalist and speechwriter officially brought into Sen. Bernie Sanders presidential campaign on Tuesday, failed to disclose his previous work with Sanders while blasting his Democratic opponents online in recent weeks, according to a report.

The Atlantic questioned the Sanders campaign about Sirota's aggressive social media posts hours before its announcement of his hiring as a senior adviser and speechwriter. Sirota frequently trashed other Democrats on Twitter, his own website and in columns in the Guardian without disclosing his work as an unofficial adviser to Sanders.

Many of his attacks were aimed at Democratic candidates Beto O’Rourke, Sens. Cory Booker of New Jersey, Kamala Harris of California, Kirsten Gillibrand of New York, and former Colorado Gov. John Hickenlooper, as well as potential candidates former Vice President Joe Biden and New York Gov. Andrew Cuomo.

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An analysis by the news magazine found Sirota had deleted more than 2,000 tweets and social media profiles after the magazine contacted him for its story. He blamed an "autodeleter that periodically and automatically deletes tweets. I started doing this many months ago,” he said in response to the Atlantic's inquiry.

On Twitter, Sirota criticized Gillibrand for endorsing former U.S. Rep. Joe Crowley, D-N.Y., before he lost in a primary against then-political novice Alexandria Ocasio-Cortez; and criticized former New York City Mayor Michael Bloomberg for his “allegedly awesome climate policies.” He also accused Harris of giving in to big donors and changing her position on health care.

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Faiz Shakir, Sanders’s campaign manager, said Sirota -- who worked as Sanders press secretary during his time in the House of Representatives (1991 to 2007) -- had been in an advisory role prior to his hiring on March 11.

“He was advising beforehand,” Shakir said. Sirota’s hiring comes amid a major staff shakeup on the Sanders campaign.

Sirota, an ardent supporter of Sanders, has become one of his most aggressive attack dogs. At one point, he said critics of the Vermont senator “are deranged and/or running a deliberate disinfo campaign.” In January, he responded to criticism online for railing against O’Rourke, who had not entered the presidential race yet, tweeting: “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,” according to the news site.

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In a December opinion piece in the Guardian, Sirota wrote that “a new analysis of congressional votes from the non-profit news organization Capital & Main shows that even as O’Rourke represented one of the most solidly Democratic congressional districts in the United States, he has frequently voted against the majority of House Democrats in support of Republican bills and Trump administration priorities.”

Capital & Main is Sirota’s website. A disclaimer at the end of the story referenced that.

Other incendiary comments made by Sirota include: "Let's hope the Boston Marathon bomber is a white American" during the investigation into the 2013 Boston Marathon bombings, of which he later doubled down in a separate piece titled, "I still hope the bomber is a white American."

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The Atlantic said Sirota’s hiring had been in discussion before Sanders launched his White House bid.

“This new job was not something I expected or planned for — but it is something I am excited to do,” Sirota wrote in his note. “I want to express my deepest thanks to all of you who have supported my journalism work over the years — your support has meant so much to me, especially in those times when my work has generated blowback from the powerful.”