Complex sentence: The case was frequently invoked in the unsuccessful attempt to pass the Wagner-Costigan Act during the presidency of Franklin Roosevelt, which would have made it a federal crime for law enforcement officials to refuse to try 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.