Rank-and-file members of the House Intelligence Committee, who are at the nucleus of the impeachment inquiry into President Donald Trump, likely have no personal aides to consult on the most sensitive information handled in the high-stakes probe.

The two Californians who lead the panel, Chairman Adam B. Schiff and ranking Republican Devin Nunes, have staff with Top Secret Sensitive Compartmented Information Security Clearance, also known as TS/SCI clearance. But other lawmakers on the committee traditionally have not had personal staff with such a clearance.

That gap could pose problems for lawmakers as they conduct the impeachment inquiry, particularly if they’re required to digest intelligence material classified at the TS/SCI level but don’t have a staff member to do so, said Daniel Schuman, policy director at Demand Progress, a nonprofit group that seeks greater government accountability.

If some parts of the impeachment inquiry pertain to matters obtained from a human or signals intelligence intercept relating to Ukraine, for example, staff without TS/SCI clearance “would have to be kicked out of such meetings” where the material may be discussed, Schuman said.

“Members of Congress are super busy and need staff to read all the documents, and that’s what TS/SCI clearance empowers staff to do,” he said.

In the absence of staff who can read primary-source material and brief lawmakers, members may have to decide on how to vote on the impeachment inquiry without consulting knowledgeable staff, Schuman said.

Schiff’s office did not immediately respond to questions on the topic.

The question of whether lawmakers serving on the House Intelligence Committee should each have at least one staff member with a TS/SCI clearance to assist the members with highly classified information has been discussed for more than three years.

In March 2016, a group of eight Democratic lawmakers serving on the committee, led by California Rep. Jackie Speier, wrote to Georgia Republican Rep. Tom Graves, then chairman of the House Legislative Branch Appropriations Subcommittee, asking for additional funding to conduct security clearance reviews.

The Democrats sought, without success, $125,000 to support security clearance reviews for personal staff. The letter writers argued that each lawmaker serving on the Senate Intelligence Committee is entitled to have one personal staff member with the TS/SCI clearance to assist with review of top secret information and that House Intelligence members needed parity.

In November, two months before becoming chairman, Schiff told CQ Roll Call that he was “committed to finding appropriate ways to meet members’ needs, and will be working with them and” the U.S. intelligence agencies “to explore how best to do so.”

Speier and Illinois Democrat Mike Quigley — who both serve on House Intelligence — told CQ Roll Call last year that they intended to press for committee members to have one personal staff member with the TS/SCI clearance. Spokespersons for both lawmakers did not immediately respond to questions for this story.

The effort thus far has only led to the House Appropriations Committee in May calling on the sergeant-at-arms to study the time taken to adjudicate security clearances for legislative staff.

The unclassified report, which would be due March 1, “may contain a classified annex which includes the average and median length of time from open to close of all security clearance requests broken down by level of security clearances (confidential, secret, top secret, and TS/SCI) so as to better provide context of timelines to Members and cleared staff,” according to the committee report accompanying the Legislative Branch appropriations bill for 2020.

In the Senate, Connecticut Democrat Christopher S. Murphy offered and then withdrew an amendment at the Appropriations Committee markup in September that would have required the Office of Senate Security to establish a procedure whereby senators who oversee highly classified government operations may ask for a TS/SCI clearance for one of their personal staff.

It’s unclear why the amendment was withdrawn.

Hundreds of thousands of executive branch employees hold TS/SCI clearances, as do many contractors who work on sensitive projects, and Congress should ensure each lawmaker has at least one staff member with similar top secret clearances, Schuman said.