▶ Watch Video: Former Vice President Mike Pence speaks out against ex-boss Trump and Florida Gov. Ron DeSantis

Washington — Three people briefed on the decision confirmed to CBS News that a federal judge in Washington ruled that former Vice President Mike Pence must testify before a grand jury about former President Donald Trump’s effort to reverse the outcome of the 2020 presidential election.

Special counsel Jack Smith, who is overseeing the Justice Department’s investigation into efforts to stop the transfer of presidential power after the 2020 election, issued a subpoena for Pence’s testimony before the grand jury in February. But the former vice president vowed to resist the demand, arguing he is protected from questioning by prosecutors under the Constitution’s “speech or debate” clause.

The provision says that members of the legislative branch “shall not be questioned in any other place” for “any speech or debate” in either chamber. Pence’s argument stemmed from his role as president of the Senate, the position held by the vice president. 

Trump also sought to block Pence’s testimony, asserting executive privilege. 

The sources told CBS News that Chief Judge James Boasberg of the U.S. district court in Washington, who is overseeing the grand jury, rejected Trump’s claims of executive privilege and found they did not apply to any potential testimony by Pence.

But Boasberg found the speech or debate clause in part protects Pence from providing testimony, specifically on congressional matters related to the events of Jan. 6, 2021, though he must testify about any illegal acts by Trump.

The scope of potential questioning of Pence by federal prosecutors before the grand jury remains unclear. Boasberg’s ruling remains under seal. Pence’s spokesman declined to comment, as did the Justice Department.

Pence could appeal the decision — he and his lawyers are deciding their next steps. The former vice president has vowed to take his legal fight over the subpoena, which he has called “unprecedented” and “unconstitutional,” to the Supreme Court. NBC News first reported the ruling.

The decision comes days after lawyers for the three parties — Trump, Pence and the Justice Department — were spotted at the U.S. district court in Washington on Thursday ahead of an expected hearing on whether the former vice president would have to comply with Smith’s subpoena.

Appointed in November by Attorney General Merrick Garland, Smith is leading the Justice Department’s two investigations involving Trump, including efforts surrounding the 2020 presidential election and attempts to interfere with the counting of Electoral College votes on Jan. 6, 2021. 

Pence presided over the joint session of Congress on Jan. 6, when lawmakers gathered to count the state electoral votes and affirm President Biden’s win. His role in the vote-counting made Pence a target of Trump’s campaign to reverse the election results, according to the House select committee that investigated the Jan. 6 assault, and the former president pressured him to unilaterally toss out or replace slates of electors from key battleground states. Pence, though, did not bow to Trump’s pressure.

The joint session on Jan. 6 was disrupted when a mob of Trump’s supporters breached the U.S. Capitol building, and Pence was moved to a secure location by the Secret Service.

He has since denounced Trump’s rhetoric surrounding the 2020 election, telling an audience of politicians and journalists this month that “history will hold Donald Trump accountable for his actions.”