Jake Sullivan, a longtime Democratic aide whom President-elect Joe Biden’s transition team tapped as the next national security adviser, was a central figure in the email scandal that rocked the final days of Hillary Clinton’s presidential campaign in 2016.

Clinton and her staffers drew intense scrutiny during the 2016 election cycle amid evidence that the former secretary of state improperly reviewed classified information in emails stored on a private server. Sullivan served as deputy chief of staff to Clinton during her time as secretary of state and later served as a top policy adviser during her campaign.

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Sullivan authored or forwarded several messages containing classified information that ended up in Clinton’s emails on the private server, Politico and the New York Times reported in February 2016. At the time, the State Department declined to comment on Sullivan’s role in the matter.

The FBI’s initial report, released in July 2016, found that Clinton and her colleagues "were extremely careless in their handling of very sensitive, highly classified information,” but had not engaged in deliberate wrongdoing. In late October of that year, the FBI reopened its probe into the private server to investigate evidence related to an investigation of Anthony Weiner, the estranged husband of former Clinton aide Huma Abedin.

The probe was reopened just days before Election Day, which culminated in President Trump’s surprise victory over Clinton. The former Democratic candidate and her allies have accused Republicans of making exaggerated claims about the email server to impact her campaign.

After a lengthy investigation into the emails, the State Department concluded in Oct. 2019 that 38 current and former staffers were “culpable” in the violation of internal security procedures. However, investigators found there was “was no persuasive evidence of systemic, deliberate mishandling of classified information.”

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The 38 current and former staffers were not identified.

The Biden transition team announced the appointment of Sullivan and several other key Cabinet positions on Monday despite an ongoing legal challenge from President Trump, who has yet to concede the election. Sullivan also served as Biden’s national security adviser when he was vice president in the Obama administration.

“We have no time to lose when it comes to our national security and foreign policy. I need a team ready on Day One to help me reclaim America’s seat at the head of the table, rally the world to meet the biggest challenges we face, and advance our security, prosperity, and values. This is the crux of that team,” Biden said in a statement. “These individuals are equally as experienced and crisis-tested as they are innovative and imaginative."