It would also be a security issue if only the state.gov server were used with classified data, which is what would have happened if clintonemail.com weren't use

It would also be a security issue if only the state.gov server were used with classified data, which is what would have happened if clintonemail.com weren't used, putting it on both state.gov and clintonemail.com servers. The fact that political officials occasionally use improper channels is something that always happens. Clintonemail.com didn't change that. The fact that it is a security issue doesn't make it prosecutable.