The FBI is responsible for more terrorism plots in the United States than any other organization. More than al Qaeda, more than al Shabaab, more than the Islamic State, more than all of them combined.
This isn't likely how you think about the FBI. You probably think of FBI agents gunning down bad guys like John Dillinger, or arresting corrupt politicians.
After the 9/11 terrorist attacks, the FBI became less concerned with gangsters and crooked elected officials. The new target became terrorists, and the pursuit of terrorists has consumed the FBI.
Every year, the Bureau spends 3.3 billion dollars on domestic counterterrorism activities. Compare than to just 2.6 billion dollars combined for organized crime, financial fraud, public corruption and all other types of traditional criminal activity.