And the Trump administration would similarly hamstring any newly created transparency organization. Not that the current congress would ever pass such a thing. And anyway, the Supreme Court has made sure that even if congress passed a law to make a(nother) government transparency agency, they can't make that agency truly independent and protected from presidential interference.

Creating an executive agency to investigate the executive would be pretty stupid. It'll likely lead to "we've investigated ourselves and found nothing", even if the president wasn't vested in all executive power, as the executive branch consolidates.

However, creating an agency in the legislative branch is another story. One of the duties of the legistive is to investigate the executive, is it not? (not that this matters when both the executive and legislative are controlled by the same party)