Congress. They were created by an act of Congress, and the only ones with oversight powers are the intelligence committee that they spied on.

> Spying on Congresspersons on behalf of the American citizenry makes sense.

Except it is explicitly illegal for them to do so. The same act that authorised the creation of the CIA - the National Security Act 1947 - also bars them from domestic spying. Anyone tasking the CIA to do so have at the very least participated in a crime, whether or not they can be charged with anything.

> If one of these Congresspersons were to go rogue and cooperate with a terroristic unit

That being so, that would fall under the remit of the FBI, Department of Homeland Security or - in the case they communicate about this with foreign interests - the NSA (!). Only if they were to do something stupid like attend in-person meetings outside US borders would it fall under the remit of the CIA, or even be legal for the CIA to pursue.

> It completely makes sense for an intel agency to spy on persons that have that type of capacity, regardless of title or location.

Not when they are barred by law from doing so, it is the responsibility of other agencies if any, and the persons they spy on are the very people tasked with providing the checks and balances against the CIA going rogue. And in fact, in this very case they were explicitly investigating claims that the CIA had committed gross violations of human rights. In that case there's a massive conflict of interest - the CIA has every reason to want to minimise their findings, and possibly even to try to strongarm them into silence.

And in fact, the CIA has repeatedly made public statements to try to discredit this report - that in itself is shocking to the extreme; in any other organizations, heads would be rolling if a department started a PR campaign against a board committee, which is the closest equivalence.

And do I have to remind you that the CIA has decades of history of horrific operations behind them, including the illegal overthrow of multiple democratically elected leaders, a long range of assassinations, dealing drugs to fund illegal operations, and more, - they've proven time and time again that they badly need more oversight. When was the last time a member of the intelligence committee went rogue again?

Well, unless you count the times they were complicit in illegal CIA cover-ups, that is.