A source familiar with the matter told CNN that former Vice President Mike Pence has been subpoenaed by the special counsel investigating Donald Trump and his role on January 6, 2021.

According to the source, special counsel Jack Smith's office is looking for documents and testimony related to January 6, CNN reported. They want the former vice president to testify about his interactions with Trump in the run-up to the 2020 election and on the day of the US Capitol attack.

The subpoena is a significant step forward in the Justice Department's two-year criminal investigation, now led by the special counsel, into Trump and his allies' efforts to obstruct the transfer of power after he lost the 2020 election.

Pence is an important witness who detailed some of his interactions with Trump in the weeks following the election in a memoir, a move that likely allows the Justice Department to override at least some of Trump's claims of executive privilege.

Emmet Flood, Pence's attorney, is known as a hawk on executive privilege, and people familiar with the discussions say Pence was expected to claim at least some limitations on providing details of his direct conversations with Trump.

Overriding claims of executive privilege

Depending on his responses, prosecutors may ask a judge to compel him to answer additional questions and override Trump's claims of executive privilege.

Pence's office refused to confirm that he had been summoned. The special counsel's office declined to comment to CNN on the matter. According to CNN, the former vice president was subpoenaed after months of negotiations.

Those familiar with the situation claimed that, Justice Department prosecutors had contacted Pence's representatives to request his testimony in the criminal investigation.

ABC News was the first to report on the subpoena. According to one source, Pence's team indicated that he was open to discussing a possible agreement with the DOJ to provide some testimony.

That request came before Smith was appointed to oversee two Trump-related investigations, one into the January 6-related probe and another into alleged mishandling of classified materials discovered at the former president's Mar-a-Lago estate.

Pence published his memoir in November, detailing some of his interactions with Trump as the former president attempted to overturn the results of his election loss to President Joe Biden. People briefed on the matter told CNN that Pence and his team were aware that the publication of the book would raise the possibility that the Justice Department would seek information about those interactions as part of its criminal investigation.

Pence declined request

Pence declined an interview request from the House select committee investigating the January 6 insurgency, but allowed top aides to testify in both the House's investigation and the Justice Department's criminal investigation. The DOJ obtained answers from top Pence advisers Greg Jacob and Marc Short in significant court victories, increasing the likelihood that the criminal investigation will extend further into Trump's inner circle.

According to a source familiar with Trump's thinking, there are no plans for Trump's team to challenge Pence's grand jury subpoena at this time.

However, if Pence declines to detail those conversations to the grand jury, Trump may still attempt to assert executive privilege over some of their conversations.