Washington: According to a person familiar with the situation, former Vice President Mike Pence testified on Thursday before a federal grand jury looking into attempts by then-President Donald Trump and his allies to rig the 2020 presidential election.

A significant turning point in the Justice Department's investigation, Pence's appearance before a grand jury in Washington examining the president he once devotedly served provides prosecutors with a crucial first-person account of specific conversations and events in the weeks leading up to the deadly insurrection at the US Capitol on January 6, 2021.

It also has important political ramifications because Pence has hinted that he might run for president in 2024 and take on Republican front-runner Donald Trump.

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The testimony came after a federal appeals court in a sealed order rejected a request by Trump's attorneys to prevent Pence from appearing, according to a person familiar with the case who insisted on anonymity to discuss a secret grand jury matter.

Earlier this year, Pence was summoned to testify, but Trump's attorneys objected on the grounds of executive privilege. The former vice president's constitutional arguments that he could not be compelled to answer questions about anything related to his role as presiding over the Senate's certification of votes on January 6 were supported by a judge in March, who declined to block Pence's appearance.

In an interview with CBS News' "Face the Nation" that aired on Sunday, Pence stated, "We'll obey the law and we'll tell the truth." And I'll tell that story in that setting just as I've been telling it to Americans all over the nation and as it is written in the pages of my memoir.

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Pence is the most prominent member of the Trump administration to be called before the grand jury, though it was not immediately clear what he may have said to the panel. Security was tight inside the federal building where the grand jury has been convening, which is only a few blocks from the US Capitol, due to Trump's appearance, and US Marshals were particularly active.

In the days leading up to January 6, Pence spoke at length about Trump's pressure campaign urging him to reject Democrat Joe Biden's victory in the presidential election, including in his book "So Help Me God." Despite Trump's assertions to the contrary, Pence, as vice president, had a ceremonial role supervising Congress' Electoral College vote count but had no authority to influence the outcome.

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Trump put his family and everyone else who was at the Capitol that day in danger, according to Pence, a former governor of Indiana and congressman, and history will hold him "accountable."

"We worked closely together for four years. Pence wrote, summarising their time in the White House, "It did not end well.

News of Pence's appearance before the grand jury broke while Trump was speaking in New Hampshire. When asked about his testimony at a diner, Trump said, "No, I'm not worried about it and I don't know anything about it."

That argument was accepted by the judge, which effectively constrained the scope of his anticipated testimony.

Jack Smith, the special prosecutor for the Justice Department overseeing the investigation, has interviewed a large number of people and sought the testimony of numerous former Trump aides, including former White House counsel Pat Cipollone and former adviser Stephen Miller.

Separately, Smith is looking into whether Trump tried to obstruct the investigation into his possible handling of hundreds of classified documents at his Mar-a-Lago estate in Palm Beach, Florida.

When either of the special counsel's investigations will be finished, or if anyone will be charged, is unknown.