Sending the letter with the powder in it is where he committed felonies that could land him real prison time.
Sounds like terroristic threats. The guy who sent those letters to the white house and several congresspeople “pleaded guilty to 13 counts of mailing a threat to injure the person of another and six counts of false information and hoaxes”
https://www.masslive.com/news/index.ssf/2018/10/daniel_frisiello_pleads_guilty.html