Second, the Constitution grants Congress the power to conduct its own investigations. Congress may hold hearings and issue subpoenas, enforceable through contempt. Congress may then use the results of its investigations — or any unwillingness of the president or his subordinates to cooperate with such investigations — to justify impeachment, to pressure the executive into taking prosecutorial action, or to inform the voting public of possible executive corruption. Thus, executive corruption may be discovered and remedied without violating the formal, structural separation between the legislative and executive branches.
That said, the manner in which Congress currently exercises its oversight authority is in dire need of reform. Note that congressional investigations into the Trump administration’s alleged ties with Russia did occur, and to a large extent the results of these investigations fell on deaf ears. With good reason, onlookers are suspicious of congressional investigations into the president as being little more than either partisan witch hunts or rubber stamps, depending on whether the president’s party controls the relevant chamber.
But Congress itself can work to obviate these concerns. Either chamber may facilitate investigation into the president by, for example, creating a bipartisan standing committee whose members are selected by opposing parties, or whose chair must belong to the party in opposition to the president. Further, Congress may delegate its investigatory authority to another body, which then reports its findings to committee or to the chamber as a whole. In fact, Congress could even have appointed Robert Mueller to investigate the Trump administration, and while Mueller would not have had prosecutorial authority, he could have enjoyed Congress’s delegated authority to issue enforceable subpoenas. Had this been the case, we would be exactly where we are now, but without the trail of process crimes and, more important, without having to discuss whether the president attempted to obstruct the investigation.