I couldn't believe he went in front of the cameras to disagree with the commander in chief. You give your opinion in private.
He was in effect trying to subvert Trump's right to call out the military if needed. It's not up to Esper to decide when it is needed. It is the President's decision.
For 200 years, the Insurrection Act has given presidents the power to deploy the military to quell unrest
https://www.washingtonpost.com/history/2020/06/03/insurrection-act-trump-history/
If our Constitution did not intend for the military to be used when needed then why does the oath say All enemies, foreign and DOMESTIC. Seems everyone is forgetting that detail.
As to General Mattis, he never had a problem with the death and maiming of our young men and women rtecting the people over seas, but has a problem protecting the American people and their property here at home. Think about that for a minute.