Earlier quoted context omitted.
The NSA is primarily charged with Signals Intelligence, Where as the CIA is Human Intelligence. So it's actually a pretty clear line. They also have their own security clearance process (though they tend to recognize each others in join work). The Department of Homeland security is a bit different, they're charged with domestic operations and support (TSA). The FBI is a Domestic Detective agency for lack of a better…
Add to this list the Secret Service for financial fraud related things (as well as protecting government officials), including credit card fraud, phone fraud (at least in the 80s), and the odd whatever-the-hell-we-feel-like-doing fear-based thing (e.g., Steve Jackson Games). Rule of thumb: If something contains the word 'Cyber' in it, it's gonna be clueless, bureaucratic and political, and utterly incompetently done.
Yet somehow Chinese and Russian cyberwar programs are pretty effective. Sounds like the US needs to catch up.