The House select committee investigating the Capitol attack on Wednesday issued a subpoena to top Trump justice department official Jeffrey Clark, escalating its inquiry into the former president’s efforts to reinstall himself in office and the 6 January insurrection.

The new subpoena underscores the select committee’s far-reaching mandate in scrutinizing the origins of the Capitol attack, as it pursues an investigation into Donald Trump’s role in pressuring the justice department (DoJ) to do his bidding in the final weeks of his presidency.

In targeting Clark, House select committee investigators followed up on a Senate judiciary committee report that last week detailed his efforts to abuse the justice department to support Trump’s attempts to overturn the 2020 election.

The House select committee chairman, Bennie Thompson, said in a statement that he authorized a subpoena for testimony from Clark to understand how the Trump White House sought to stop the certification of Joe Biden’s election victory during the joint session of Congress.

“We need to understand Mr Clark’s role in these efforts at the justice department and learn who was involved across the administration. The select committee expects Mr Clark to cooperate fully with our investigation,” Thompson said.

The new subpoena targeting Clark came a day before the select committee was scheduled to conduct depositions against top Trump administration officials over their potential role in the 6 January insurrection and what they knew in advance of the Capitol attack.

But it was not clear hours before the deadlines whether the Trump officials – former White House chief of staff Mark Meadows, deputy chief of staff Dan Scavino, strategist Steve Bannon and defense department aide Kash Patel – would testify on Thursday and Friday.

The Guardian first reported that the Trump aides were expected to largely defy the subpoenas for documents and testimony under instructions from the former president and his legal team led by the ex-Trump campaign lawyer Justin Clark.

Trump instructed his former aides to defy the subpoenas issued under the threat of criminal prosecution on grounds of executive privilege, in an attempt to slow-walk the select committee’s investigation, according to a source familiar with the strategy.

The select committee had said in a recent statement that Meadows and Patel were “engaging” with House investigators ahead of the deposition dates, but declined to comment on the extent of their cooperation. Bannon has vowed to defy his subpoena in its entirety.

The House select committee investigators’ demand for testimony from Clark amounts to a significant development for the second investigative track pursued by the panel – in addition to their investigation into the organization of the Capitol attack.

The select committee had sought to negotiate with Clark for voluntary testimony but a breakdown in discussions led Thompson to move ahead with a subpoena compelling a deposition under oath, according to a source familiar with the matter.

The Senate report, among other things, described how justice department officials and Trump’s White House counsel scrambled to stave off pressure during a period when Trump was being told about ways to block Biden’s certification by a lawyer he saw on television.

Senator Dick Durbin, the chairman of the Senate judiciary committee, said the report’s findings led him to believe that Trump – who is expected to run for the presidency in 2024 – would have “shredded the constitution to stay in power”.

The report reaffirms previous accounts of Trump’s attempts to return himself to the Oval Office. But in drawing on testimony from the former attorney general Jeffre Rosen and his deputy, Richard Donoghue, it brought new light to Clark’s role in the conspiracy.

Clark in particular played a leading role in seeking to overturn the results of the 2020 election, having participated in multiple conversations with Trump about how to upend the election and pushed his superiors to entertain debunked claims of fraud, the report said.

The Senate judiciary committee report detailed a 2 January confrontation during which Clark demanded that Rosen send Georgia election officials a letter that falsely claimed the DoJ had identified fraud – and threatened to push Trump to fire him if he refused.

In a subsequent 3 January meeting in the Oval Office, Trump appeared to entertain the threat against his acting attorney general: “One thing we know is you, Rosen, aren’t going to do anything to overturn the election,” Rosen recounted Trump saying.