The House select committee investigating the Capitol attack is confronting a pivotal moment as resistance from top Trump administration aides threatens to undermine their efforts to uncover the extent of the former president’s involvement in the 6 January insurrection.

The select committee remains in the evidence-gathering phase of the investigation that now encompasses at least five different lines of inquiry from whether Donald Trump abused the presidency to reinstall himself in office or coordinated with far-right rally organizers.

But unless House investigators can secure a breakthrough to obtain documents and testimony from Trump’s White House chief of staff, Mark Meadows, and others in the next few weeks, the most pressing questions about Trump’s role in 6 January may go unanswered, two sources said.

The select committee has designated its “gold” team to examine the extent of Trump’s personal involvement in the events that left five dead and more than 140 injured as his supporters stormed the Capitol in his name, the sources said.

One major focus of the investigation is whether Trump had advance knowledge of the insurrection, the sources said – since if they uncover evidence of conspiracy to violently stop the certification of Joe Biden’s election win, that could constitute a crime.

But to make that kind of case, which would then guide Congress on how to draft laws to avert a repeat of the Capitol attack, may be impossible without clear insight into Trump’s movements inside the White House both on 6 January and the days before, the sources said.

The select committee, the sources said, effectively needs to know what Trump’s top aides know about what the former president thought would allow him to remain in office – and whether that extended to encouraging surrogates to physically stop the certification.

To that end, House investigators last month subpoenaed Meadows, his deputy, Dan Scavino, former chief strategist Steve Bannon and defense department aide Kash Patel, while asking the National Archives to turn over Trump White House records.

Meadows is of special interest since he remained by Trump’s side as the Capitol attack unfolded and, in the final weeks of the administration, sat in on 6 January strategy meetings with the former president.

The former chief strategist Bannon was similarly subpoenaed for documents and testimony as he was in constant contact with Trump in the days before the Capitol attack, and played a major role in drawing up the legal arguments for Pence to return Trump to office.

Bannon also appeared to have prior knowledge of the Capitol attack, which former White House aides say would not have escaped Trump’s attention. “All hell is going to break loose tomorrow,” Bannon said on his War Room podcast the day before the insurrection.

The select committee, meanwhile, also asked the National Archives for Trump White House materials since they are the custodian for visitor logs and Oval Office memoranda – records that could shed light on the interactions Trump was having with Meadows and Bannon.

But under orders from Trump to defy the subpoenas on grounds of executive privilege, the select committee is yet to obtain any materials or testimony from the four aides, while the National Archives is unable to release records until Trump’s lawsuit on the issue is resolved.

The collective efforts from Trump and his aides mean that unless House investigators can find a way to circumvent the logjam, the gold team may ultimately find themselves unable to ever uncover whether 6 January was a White House-sponsored insurrection.

Bannon, for instance, was last week referred to the justice department for prosecution after he defied his subpoena in its entirety, but a source at the US attorney’s office cautioned a decision on his case could take months of deliberations.

The delay stems in part from the fact that the justice department is now examining whether they can successfully secure an indictment in the Bannon case and are indifferent to the select committee’s need to finish a report before the 2022 midterms, the source said.

The US attorney’s office, the source added, may not be able to proceed with a potential prosecution against Bannon until the justice department first resolves other constitutional complaints raised by Trump in his lawsuit against the National Archives.

Taken together, staff on the gold team are now starting to think the most likely avenue for securing Trump White House materials is not through the former president’s aides but through the National Archives request, since Biden has the final say over executive privilege.

Still, given Trump’s pending lawsuit lodged against the National Archives – a move described by a source close to the Trump legal effort as a way to stymie the investigation – the select committee may run out of time before being able to examine the materials.

Tim Mulvey, a spokesperson for the select committee, on Friday rejected the internal concerns, saying in a statement: “While we don’t comment on the specifics of our investigation, we are moving ahead expeditiously to uncover the facts, get answers for the American people, and make legislative recommendations to help ensure nothing like January 6th ever happens again.”

“The select committee won’t be derailed by those seeking to obstruct our investigation, and we won’t be distracted by anonymous sources posing as experts and insiders,” Mulvey added.

The select committee’s struggle to enforce orders against the Trump aides shows the lack of teeth carried by congressional subpoenas, with its power systematically eroded by a Trump administration that has found, since 2016, that defiance carries scant penalties.

But the difficulty in obtaining any formal Trump White House materials – either through the former president’s aides or even through the National Archives – also underscores how what could be the most consequential lines of inquiry appear to be dangling by a thread.

The select committee has had success eliciting information elsewhere, most notably with individuals connected to the Trump-supporting Women for America First organization that planned the 6 January “Stop the Steal” rally subpoenaed earlier in October.

House investigators also heard voluminous testimony from Trump’s former acting attorney general Jeffrey Rosen over seven hours of voluntary testimony, that could help the gold team establish whether the former president unlawfully pressured the justice department.

But without knowing what Trump’s top aides know of the former president’s connections to the Capitol attack, the sources said, it could mean that Congress is left unable to write legislation to avert a different effort to stop the certification in 2024.