Little is known about what, exactly, goes on behind the locked doors that lead into the committee’s offices. But now, interviews and emails obtained by BuzzFeed News lay bare the numerous hurdles the secretive committee has faced in its mission to obtain and decipher troves of banking records that could shed more light on the Russian scheme — and whether the current president had anything to do with it.

Treasury has at times been reluctant to cooperate with the committee’s requests for sensitive financial documents that are significant to the Russia probe, at one point going at least four months without responding to one of the committee’s requests.

Last year, Treasury rejected the committee’s request for help from one of its experts, even as Treasury officials have speculated — behind closed doors — that the Senate committee would not be able to follow the twisting financial trail laid out in the documents they had turned over, a path that often passes through offshore shell companies or untraceable cash transactions.