Complex sentence: The case was to be evoked in the unsuccessful during the Presidency of Franklin Roosevelt called the Wagner-Costigan Act to make it a federal crime for law enforcement officials to refuse to take steps to prevent a lynching.
Split into simpler sentences: The case was frequently invoked in the unsuccessful attempt to pass a law called the Wagner-Costigan Act during the Presidency of Franklin Roosevelt. This would have made it a federal crime for law enforcement officials to refuse to take steps to prevent a lynching.