“„“While most witnesses with relevant information appear before Congress voluntarily, in some cases, it is necessary to compel their testimony,” said Rep. Nadler. “It is simply not prudent to rely on the voluntary promise to appear of a witness who already has broken such an agreement. I hope that it will not become necessary to issue this subpoena, but Congress has the prerogative and duty to conduct meaningful oversight to ensure a robust system of checks and balances.”