I just saw on TV, the FBI gave no reason for firing him.
His lawyer says it can't be the private messages he sent. I had already written the below that it can't be the messages, when I saw this on TV, 11:07 am. Here is what I was writing when I saw this on TV:
The problem they had in trying to fire him was, it is not against the law, or rules of the Justice Department, to send a text or email to someone and express a personal opinion about a candidate for president or a sitting president or the fact you hate broccoli. I haven't researched to find their stated reason(s) for this firing, but it can't be due to those messages; it has to be an action he took that violated their rules. (Now, there is no reason to search for the reasons, as the FBI didn't give any.)
If you on this thread have a job, you can send personal texts, emails, to anyone you want to express your opinion on a subject, including whatever is happening in your company. It is called, freedom of speech. Now, if you send the president of your company a message that you hate his guts, the outcome of that is, you may lose your job. It wasn't a law or rule you broke, it was your less than smart message to your company president.