Due process is the only way.
It is about time. Since the FBI, National Security, and IRS have not offered any information on their own; it must be extracted from them. The Emolument Constitutional Violation case is in the judicial process now, whereby attorneys are requesting all documents.
"Rep. Jerrold Nadler (D-N.Y.) filed a “resolution of inquiry” Thursday, a relatively obscure parliamentary tactic used to force presidents and executive-branch agencies to share records with Congress. Under House practice, such a resolution must be debated and acted upon in committee or else it can be discharged to the House floor for consideration.
Nadler’s resolution asks Attorney General Jeff Sessions to provide “copies of any document, record, memo, correspondence, or other communication of the Department of Justice” that pertains to any “criminal or counterintelligence investigation” into Trump, his White House team or certain campaign associates; any investment made by a foreign power or agent thereof in Trump’s businesses; Trump’s plans to distance himself from his business empire; and any Trump-related examination of federal conflict of interest laws or the emoluments clause of the Constitution."
It is just a matter of time and due process.