Welcome! Gave me a few hours of needed relief!
I was kinda expecting this, after the President apparently caught Mattis off guard with his announcement. I have had a lot of respect for Mattis, so I am sort of sad to see him go.
I needed a magnifying glass to see the writing on the letter at the link below:
“Because you have the right to have a Secretary of Defense whose views are better aligned with yours on these and other subjects, I believe it is right for me to step down from my position,” the letter said.
http://www.wflx.com/2018/12/20/secretary-defense-mattis-retire-feb-trump-tweets/