This is a first. Mattis' statement was to be expected, perhaps, but Esper must have thought he should jump ship while still retaining some sliver of self-respect.
"Donald Trump is the first president in my lifetime who does not try to unite the American people — does not even pretend to try. Instead he tries to divide us. We are witnessing the consequences of three years of this deliberate effort. We are witnessing the consequences of three years without mature leadership."
— Former Secretary of Defense Jim Mattis
"I say this not only as secretary of Defense, but also as a former soldier and a former member of the National Guard, the option to use active-duty forces in a law enforcement role should only be used as a matter of last resort, and only in the most urgent and dire situations. We are not in one of those situations now. I do not support invoking the Insurrection Act."
— Imminently former Secretary of Defense Mark Esper