District courts are responsible for handling what percentage of federal court cases?

District courts play a crucial role in the federal judiciary system as they are tasked with the majority of federal court cases. In fact, they handle approximately 90% of all federal cases. This percentage stems from the fact that district courts serve as trial courts where most federal legal disputes begin, covering a wide range of issues including civil rights violations, federal crimes, and cases involving federal statutes.

The significant volume of cases processed at this level reflects the district courts' primary function in adjudicating disputes before any potential appeals can be made to higher courts, like the circuit courts of appeal. Consequently, district courts serve as the foundational layer of the federal court system, managing all cases unless specifically assigned to specialized courts.

Other options representing lesser percentages do not accurately reflect the role district courts play within the judicial system. Thus, the correct answer underscores the extensive responsibility that district courts bear in handling federal cases, which is around 90%.