The FBI and CIA are at odds again over the FBI being able to recruit and use spies overseas. Since the CIA was created, the FBI could only seek out and hire spies (informants) in the United States, while the CIA could only do it overseas. Actually, the CIA could seek out, and hire Americans or foreigners within the U.S., for spying overseas. But otherwise, the CIA could no engage in espionage against American within the U.S. This has caused problems in the past, particularly when looking for Russian spies. Thats the FBIs job, at least inside the United States. But the Russians moved their spies around a lot, and the CIA and FBI often had fat files on the same Russian agents. The CIA and FBI was supposed to cooperate in this area, but often that did not happen. Sometimes it was just the usual confusion when two bureaucracies try to coordinate efforts. At other times, one agency did not trust the other to keep secrets.
The failure to get the information to where it was needed before September 11, 2001 was mainly a coordination problem. The CIA knew about some of the 911 terrorists, but the FBI dropped the ball when it came to investigating and making arrests, or dragging the latest stuff out of the CIA. Despite Congressional restrictions on how the CIA runs its espionage operations, the CIA is blamed for not having a better idea of what Islamic terrorists were up to before 2001. So the Department of Defense and FBI are going to be allowed to run their own spies overseas. The attitude appears to be; better to have too many spies, than too few. All three agencies are supposed to coordinate their efforts, but no one expects that to work perfectly every time. The consensus is that things wont get any worse. Perhaps.
Other nations have had similar problems. For decades after World War II, the Soviet Union had two different organizations running spies overseas. Most of the effort was from the KGB (a sort of combined CIA/FBI/Border Patrol/Coast Guard/Etc.) and a much smaller GRU (military intelligence). GRU was thought to be more dangerous, perhaps because they were a smaller operation and hustled a bit more as a result. Having two Soviet spy agencies to worry about did make counterintelligence more difficult.
The British adopted a different approach. They also have two intelligence agencies; MI 5 for work inside the United Kingdom, and MI 6 to deal with foreign stuff. When working on a particular case, either of these agencies could do wherever they had to. Which meant that sometimes MI 5 people went overseas, and sometimes MI 6 agents were operating inside Britain. This has worked well for many decades.
Before World War II, the FBI had visions of running espionage operations overseas. But that never happened, partly because many Americans did not want to see an intelligence organization that powerful in the United States. So the new intelligence system in the United States developed to keep everyone happy, or at least less scared.