A former top FBI lawyer steeped in the Russian investigation joined Twitter.

James Baker, who was general counsel for the bureau during the period surrounding the 2016 election, was welcomed by the social media giant's top lawyer Monday evening.

"Thrilled to welcome @thejimbaker to @Twitter as Deputy General Counsel. Jim is committed to our core principles of an open internet and freedom of expression, and brings experience navigating complex, global issues with a principled approach," said Twitter general counsel Sean Edgett.

"Thanks @edgett!! I'm very excited to join such a great team @Twitter doing such important work. Glad to be on board," Baker tweeted back.

Baker is joining Twitter weeks after the company stirred controversy by slapping fact-checking labels on some of President Trump's tweets. Trump signed an executive order on May 28 aimed at weakening the legal protections of social media companies.

Twitter was one of the social media platforms used by a Kremlin-linked troll farm to interfere in the 2016 election, special counsel Robert Mueller found in his investigation.

Baker is a person of interest in inquiries into the Russia investigation. Senate Judiciary Committee Chairman Lindsey Graham listed Baker as one of the dozens of Obama and Trump administration officials he might seek testimony from as part of his Crossfire Hurricane investigation. The South Carolina Republican was granted subpoena power in that investigation last week by a party-line vote.

Baker was involved in the sign-off process of at least the first Foreign Intelligence Surveillance Act warrant application targeting onetime Trump campaign adviser Carter Page.

Inspector General Michael Horowitz released a report in December that criticized the Justice Department and the FBI for at least 17 “significant errors and omissions” related to FISA warrants against Page in 2016 and 2017 and for the bureau's reliance on British ex-spy Christopher Steele’s salacious and flawed dossier. Steele put his research together at the behest of the opposition research firm Fusion GPS, funded by Hillary Clinton's presidential campaign and the Democratic National Committee.

Horowitz noted in his report that “certain former FBI employees who agreed to interviews, including [FBI Director James] Comey and Baker, chose not to request that their security clearances be reinstated for their OIG interviews.” That meant that the inspector general was “unable to provide classified information or documents to them during their interviews to develop their testimony, or to assist their recollections of relevant events.” Baker worked directly under Deputy Director Andrew McCabe from July 2016 through May 2017 during the Crossfire Hurricane investigation.

The DOJ watchdog said Baker “told us that he also remembered being satisfied at the time that there was probable cause articulated in the draft application to believe that Carter Page was an agent of a foreign power," yet “it was difficult for him to fully explain to us the basis for his assessment without reviewing the entire application again, but that he recalled Page's continuing relationships with Russian intelligence officers, even after the FBI made Page aware that they were Russian intelligence officers, being 'key' facts in his mind.”

“Baker said that in this case, he asked to read the application because he recognized its sensitivities, including that the target had been associated with a presidential campaign and that the whole case was about Russian efforts to influence the presidential election and whether those efforts included any interactions with the Trump campaign,” Horowitz wrote. “He said that he expected that the FBI would be called upon after-the-fact to justify its actions, and he wanted to ensure that his significant FISA experience was 'brought to bear' on the application.”

Footnotes from Horowitz’s report declassified in April showed that Steele's dossier might have been compromised by Russian disinformation in 2016. FBI investigators received information in 2017 “indicating the potential for Russian disinformation influencing Steele’s election reporting” that was seemingly related to the biggest unverified claims in Steele’s dossier. Page was never charged with any wrongdoing.

Baker, who became general counsel in 2014, defended the Russia investigation and the FBI’s handling of Steele's dossier. During an interview with Yahoo News, he said, “we took it seriously,” but “we didn’t necessarily take it literally” and did not treat it as “literally true in every respect.”

A Washington Post report in late 2017 said Baker was being reassigned away from the general counsel role as one of Christopher Wray's first moves as director of the bureau. He was under criminal investigation for allegations that he leaked unauthorized information to the media.

Baker resigned in May 2018 and joined Lawfare, a national security blog affiliated with the Brookings Institution whose editor-in-chief is Benjamin Wittes, a friend of Comey. He later joined the R Street Institute and then CNN as a legal analyst. Baker is no longer working at the cable news network, a CNN source told the Washington Examiner.

Mike Brest contributed to this report.