I hold an SAP clearance. What most people aren't even discussing here is that there are very strict rules for where classified data can be stored or discussed.

No computer that contains classified data can ever be connected to any unclassified network. There can never be any physical connection between an unclassified and classified network.

Additionally, people who are cleared to a classified program cannot even verbally discuss classified information if they are not in a secured classified room/area where they have to sign in and out of. In these rooms, any device that has electronic memory is not permitted to be carried (flash drives, cell phones, smart watches, etc.). If I forgot to take my phone out of my pocket before entering a classified room, my phone would never be able to leave that room and would likely be destroyed.

Any physical classified information must also remain in these rooms except for specific instances where strict currier rules are in effect.

If I violated any of these rules, through negligence, I would at a minimum lose my security clearance.

For Clinton to have transferred classified information to an unclassified computer, she must have actively violated multiple rules. She must have either connected a classified network to her private network and transferred the emails, or brought an unclassified electronic storage device into a classified room, connected it to a classified computer, transferred the information, then taken the data to her private unclassified computer.

If ever did this, I would lose my security clearance and job, face prison time, and probably be investigated for espionage.

So to answer your question, this is VERY serious and something that she should be criminally charged for.