WASHINGTON — Former Vice President Mike Pence testified Thursday before a federal grand jury investigating efforts by then-President Donald Trump and his allies to overturn the results of the 2020 presidential election, according to a person familiar with the matter.

Pence’s appearance before a grand jury in Washington scrutinizing the president he once loyally served is a milestone in the Justice Department’s investigation and likely gives prosecutors a key first-person account about certain conversations and events in the weeks preceding the deadly Jan. 6, 2021, insurrection at the U.S. Capitol. It also carries significant political implications, coming as Pence hints at entering the 2024 presidential race and a potential run against Trump, the Republican front-runner.

The testimony, confirmed by a person familiar with the matter who insisted on anonymity to discuss a secret grand jury matter, came hours after a federal appeals court in a sealed order rejected a bid by Trump’s lawyers to block Pence’s appearance.

Pence was subpoenaed to testify earlier this year, but Trump’s lawyers objected, citing executive privilege concerns. A judge in March refused to block Pence’s appearance, though he did side with the former vice president’s constitutional claims that he could not be forced to answer questions about anything related to his role as presiding over the Senate’s certification of votes on Jan. 6.

“We’ll obey the law, we’ll tell the truth,” Pence said in an interview with CBS News’ “Face the Nation” that aired Sunday. “And the story that I’ve been telling the American people all across the country, the story that I wrote in the pages of my memoir, that’ll be the story I tell in that setting.”

It was not immediately clear what Pence may have told the grand jury, but he is the most high-profile Trump administration official to be summoned before the panel. Inside the federal building where the grand jury has been meeting, just blocks from the U.S. Capitol, security was high throughout the day because of Pence’s appearance.

Pressure to Overturn Election Results

Pence has spoken extensively about Trump’s pressure campaign urging him to reject Democrat Joe Biden’s presidential election victory in the days leading up to Jan. 6, including in his book, “So Help Me God.” Pence, as vice president, had a ceremonial role overseeing Congress’ counting of the Electoral College vote but did not have the power to affect the results, despite Trump’s contention otherwise.

Pence, a former Indiana governor and congressman, has said that Trump endangered his family and everyone else who was at the Capitol that day, and history will hold him “accountable.”

Related Story:

“For four years, we had a close working relationship. It did not end well,” Pence wrote, summing up their time in the White House.

Trump was speaking in New Hampshire when news broke of Pence’s grand jury appearance, but he did not mention it.

Pence Challenged Subpoena

Lawyers for Pence had raised their own, more narrow challenge to the subpoena. They argued that because Pence was serving in his capacity as president of the Senate as electoral votes were being counted in Congress on Jan. 6, he was protected from being forced to testify about that process under the Constitution’s “speech or debate” clause, which is intended to protect members of Congress from being questioned about official legislative acts.

A judge agreed with that argument, effectively narrowing the scope of his expected testimony.

The Justice Department special counsel leading the investigation, Jack Smith, has cast a broad net in interviews and has sought the testimony of a long list of former Trump aides, including ex-White House counsel Pat Cipollone and former adviser Stephen Miller.

Smith is separately investigating Trump over the potential mishandling of hundreds of classified documents at his Palm Beach, Florida estate, Mar-a-Lago, as well as possible efforts to obstruct that probe.

It is unclear when either of the special counsel’s investigations will end or who, if anyone, will be charged.