Committees shouldn’t wait for DOJ to reject a document request or hide behind tried and tested excuses like “sorry, it’s an ongoing investigation so we can’t help you,” because those are dilatory tactics designed to obstruct congressional investigations. Instead, go straight to the source of the records being sought and get them yourself.
Subpoena the banks, subpoena the telecommunications companies, subpoena Big Tech and subpoena all the business associates. On the heels of the January 6 Committee, it’s literally impossible to issue too many subpoenas.