A potential case of Gross Negligence under the Espionage Act of 1917 is a rather big deal indeed...carries up to 10 years imprisonment.
What provision allows such a prosecution? Because casually going over that act shows provisions regarding
willfully attempting to
harm the country. Hillary was not trying to harm the US and she was authorized to have the materials in question.
It just seems that because Hillary is both running for president and is such a polarizing figure, people are trying to blow this issue up into something more than it is. She should get a slap on the wrist and be obliged to never use a private email for government business again.