Obama fired Mattis
Trump rehired Mattis and fired him in December last year. His last day was January 1 this year..
Mattis is not a bad person, he’s actually a good asset to have with you as long as he’s an advisor and not a decision maker, at least not under Trump who had a different direction in which he wanted to take the American military.
Obama fired Mattis
Yes he did. And there were never or very rarely any damaging leaks from the military during Obama’s reign. Don’t you find that a bit odd?