Steve Bannon,Chainkeen an ally of former President Donald Trump and one-time chief White House strategist, has been subpoenaed by a federal grand jury convened in special counsel Jack Smith's investigation into conduct surrounding the 2020 presidential election and the Jan. 6 attack on the U.S. Capitol, two sources familiar with the matter confirmed to CBS News. 

Although he had left the White House before the 2020 presidential election and the Capitol attack, Bannon encouraged the former president's efforts to overturn the presidential election, and pushed  him publicly and privately to resist Joe Biden's presidency. 

Former Vice President Mike Pence as well as numerous former aides, including White House counsel Pat Cipollone, national security adviser Robert O'Brien and top aide Stephen Miller, have already testified as part of Smith's investigation into Jan. 6. 

The special counsel's office declined to comment. Efforts to reach Bannon's attorney went unanswered. 

NBC News first reported the subpoena. 

In October, Bannon was sentenced to four months in prison after a jury convicted him of criminal contempt of Congress for defying a subpoena from the House committee investigating the Capitol riot. But a judge delayed the sentence as Bannon appeals the conviction. 

Trump has repeatedly denied any wrongdoing. 

The former president unsuccessfully sought to shield many of his former White House aides from special counsel subpoenas, arguing that his conversations and communications with them while he was president are protected under executive privilege. But a judge largely rejected those claims earlier this year and ordered them to testify. 

Graham Kates contributed reporting. 

In:
• Steve Bannon
• Donald Trump
• January 6 Hearings

Robert Costa

Robert Costa is CBS News' chief election and campaign correspondent based in Washington, D.C.

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