Jess, you posted...
Mattis worked for the American people and the Constitution and was legally bound to support the President that the American people had lawfully elected.
Let’s agree he failed to support the President, as you say.
But, Mattis wasn’t fired by the “the Americans,” he was fired by the president.
I would say, in that case, he worked “FOR the president.”
Wasn’t he fired by two presidents?
He worked for the President, who works on behalf of the people, who elected him as Commander-in-Chief.