The only reason General Mattis has remained silent about Trump's witheringly destructive behaviors is the military tradition of not contradicting one's "commander-in-cheif."
However, Mattis has also made clear that once Trump is out of office, Mad Dog will spill the beans. All the beans.
Even so, Mattis has already had this to say.
In Stern Rebuke To Trump, Gen. Mattis Sees "Storm Clouds Gathering" And America "Withering"
https://paxonbothhouses.blogspot.com/2019/08/in-stern-rebuke-gen-jim-mattis-sees.html
Jim Mattis Describes Trump As A Dolt Who Does Not Read And Has No Interest In Learning
https://paxonbothhouses.blogspot.com/2019/09/jim-mattis-describes-trump-as-dolt-who.html
Three Laugh-Out-Loud Moments: Mattis, Borowitz, Pacino-Mueller
https://paxonbothhouses.blogspot.com/2019/10/three-laugh-out-loud-moments-mattis.html
As for holier-than-thou-elitists:
Reprise: "Wow. What A Concept! If You Study, You'll Actually..."
https://paxonbothhouses.blogspot.com/2019/10/reprise-wow-what-concept-if-you-study.html