Responsibilities of various pieces of the federal government are usually well-delineated but without clean taxonomic hierarchy. The hierarchy only gets cleaned

Responsibilities of various pieces of the federal government are usually well-delineated but without clean taxonomic hierarchy. The hierarchy only gets cleaned up years or decades after things get spun up and it takes a massive reorganization effort. Single entities with two (or more) responsibilities often aren't worth the effort needed to split up, and thus never fall anywhere cleanly. Even to this day the department that investigates counterfeit currency is also responsible for bodyguarding the president.