The fox in the hen house is investigating why the chickens are missing. The eggs - since they're quiet - will be found at fault. The fox stays fat, the chickens are happy, it's a win/win down on the farm.
A part of Congress' job is oversight of government agencies. Investigations are for allegations of criminal wrongdoing and involve a special prosecutor.
I think it's total derilection of duty for Dem Congressmen to refuse to participate in Congressional committees and demand special investigators for situations that don't call for them.
For instance the Senate Ethics Committee was shut down for over a year because the Dems wouldn't participate. The irony is the Ethics Committee is one of the most feckless. It's non-functional by design containing an equal number from both parties so one side can't bbq the other and business as usual can continue.