The penalty for passing secrets after one's employment in the agency ends should be mandatory exile or death - and no one who is exiled can take a nickel of their money out of the US.
There should be oversight at all times by citizens groups that have the power to investigate and recommend indictments. The legal process in adjudicating these matters cannot involve a singe government employee, and should have a five judge panel with a civilian jury specifically educated to know breach of law.
No government agency should be allowed to do their own hiring, or have any input into hiring. They should submit job skill set criteria, and then the hiring will be done by revolving civilian employment agencies - all vetted and on oath to not have connections to government or foreign entities (penalty for lying = exile or death).
The assumption when fashioning anything government should be that government jobs attract ideologues, narcissists, and criminals.
Of course, there would have to be much more involved to ensure agencies did not become self-serving self-perpetuating problems.
“Intelligence agencies, as a necessary evil, should only exist in 20 year blocks, then be replaced with another.”
They are an anathema to a free society where the Government is loaned power from the people. We did not have them until our government was contaminated by British input from WWII.
We had military intelligence that was focused on foreign military capabilities and actions.
Intelligence agencies in the British model which we have do everything in secret. The secrecy -directly- causes that agency to become despotic. The reason is that they believe they have superior information that is not available to the public. So for reasons we are not allowed to know, they begin to decide everything FOR us. And then next step is manipulating the population to achieve what they think is important. This unleashes a firehose of propaganda.
They do not have a place in a republic.