Congressman Bennie Thompson, the chairman of the new House select committee to scrutinize the Capitol attack, says he will investigate Donald Trump as part of his inquiry into the events of 6 January – a day he sees as the greatest test to the United States since the civil war.

In an interview with the Guardian, Thompson said that he is also prepared to depose members of Congress and senior Trump administration officials who might have participated in the insurrection that left five dead and nearly 140 injured.

“Absolutely,” Thompson said of his intent to pursue a wide-ranging inquiry against the former president and some of his most prominent allies on Capitol Hill. “Nothing is off limits.”

The aggressive move to place Trump in the crosshairs of the select committee underscores Thompson’s determination to uncover the root causes of 6 January, even after Senate Republicans, fearing political damage, blocked the creation of a 9/11-style commission.

The move comes at the same time as many Republicans have been seeking to downplay the attack on the Capitol – in which five people died – or, in the case of Trump himself, cast its protagonists in a more positive light.

But there is no doubt in Thompson’s mind of the seriousness of the event. Addressing some of the key questions at the heart of the select committee’s investigation into the attacl, Thompson characterized the inquiry as an undertaking to safeguard the peaceful transition of power and the future of American democracy.

“The issues of January 6 are one of the most salient challenges we have as a nation, to make sure that this democracy does not fall prey to people who don’t really identify with democracy,” Thompson said.

The central thrust of the investigation will focus on the facts and circumstances surrounding the Capitol attack, Thompson said, and the first hearing scheduled for 27 July will feature current and former US Capitol police and DC Metro police officers.

But in pursuing a broad mandate to also examine the root causes of the insurrection, Thompson reiterated that he remains prepared to issue subpoenas to compel testimony from an array of Trump officials connected to the attack should they refuse to appear voluntarily.

Trump and McCarthy among top witnesses

Thompson indicated that Trump and the House minority leader, Kevin McCarthy, are among the top witnesses for his investigation, in large part because McCarthy was on the phone with the former president as the riot unfolded.

McCarthy called Trump in a panic as rioters breached the Capitol and begged him to call off his supporters, only for Trump to chastise the top Republican in the House for not doing more to overturn the results of the 2020 presidential election.

“There will not be a reluctance on the part of the committee to pursue it,” Thompson said of McCarthy’s call. “The committee will want to know if there is a record of what was said.”

The exchange between McCarthy and Trump is of singular importance, since it provides a rare window into what Trump, sequestered in the West Wing, was privately thinking and saying as the Capitol was invaded.

But Thompson went further, and said that he expects anyone – whether a sitting member of Congress or former White House official – who may have spoken to Trump on 6 January to become the subject of the select committee’s investigation.

That prospect took on added significance on Monday, after McCarthy named House judiciary committee chairman Jim Jordan as one of his picks for the panel. Jordan has previously suggested he may have also spoken to Trump as the assault took place.

“If somebody spoke to the president on January 6, I think it would be important for our committee to know what was said. I can’t imagine you talk about anything else to the president on January 6,” Thompson said.

He also warned Republicans against attempting to stymie the committee’s investigation, saying that it had no deadline to furnish a report and as a result, would be immune to delay tactics previously deployed during the first Trump impeachment inquiry.

“Notwithstanding elections next year, we will not stop until our investigation is complete,” Thompson said.

Subpoenas to be enforced in court

Against that backdrop, Thompson said he expects to demand testimony from senior Trump administration officials who were in the Oval Office as the riot unfolded, from the then White House chief of staff, Mark Meadows, to Trump’s daughter Ivanka.

If Trump administration officials refuse to appear before the committee, citing executive privilege, Thompson said he would issue subpoenas and launch lawsuits to enforce his congressional oversight authority.

“We will pursue it in court,” he said.

Thompson added that he expects the select committee and senior House investigators to meet with the attorney general, Merrick Garland, and expressed optimism for conducting his investigation in close coordination with the justice department.

He was adamant that his investigation would not overlap with existing criminal probes opened by the justice department and the US attorney for the District of Columbia. Still, he said he hoped the DoJ would cooperate with his inquiry.

“We don’t want to get in the way of indictments,” Thompson said. “But I think there could be some sharing of information that could be germane to our investigation, just like other committees have negotiated in the past.”

Thompson said that although no date has been set for a meeting with the attorney general, it will involve the 6 January select committee’s members and senior staff. The senior staff may be named as soon as this week, according to a source familiar with the matter.

To emphasize his seriousness, Thompson said the select committee would draw on legal counsel and investigative staff from existing House panels as well as the US intelligence community – including the NSA, CIA and FBI.

Thompson also said he expects the National Archives, the agency now in possession of records from the Trump White House, to make materials available for his investigation. “That should not be an issue,” he said, though he left open the possibility of subpoenas in the event of noncompliance.

And he vowed to refer criminal charges should Trump White House records, covering the period from the November election through 6 January, be missing or destroyed – a persistent worry among Democrats as Trump grew increasingly unhinged in the final weeks of the administration.

“That violates the law,” Thompson said. “I don’t see any hesitation on our part to pursue that. If the respect for the rule of law is not adhered to, that’s even more reason for this select committee to exist.”