I anticipate being asked questions about the letter released by General Mattis. I will paste in and comment on every section.

In Union There Is Strength
I have watched this week’s unfolding events, angry and appalled.
The words “Equal Justice Under Law” are carved in the pediment of
the United States Supreme Court. This is precisely what protesters are
rightly demanding. It is a wholesome and unifying demand—one that
all of us should be able to get behind. We must not be distracted by a
small number of lawbreakers. The protests are defined by tens of
thousands of people of conscience who are insisting that we live up to
our values—our values as people and our values as a nation.

Of course, every reasonable American, especially veterans, are behind “Equal Justice Under Law”. Reasonable people, including President Trump, agree that protestors are rightly demanding this. He stated as much. Not sure if General Mattis missed that. Mattis is also correct that we should not become distracted from “Equal Justice Under Law”. I know I am not distracted. However, I am also not a prisoner of two ideas. You can be for “Equal Justice Under Law” and clearly see the mass devastation caused by the “small number of lawbreakers”. It is like General Mattis is saying you must only pay attention to one thing. Hard to believe that is coming out of the mind of a former general of such great renown.

When I joined the military, some 50 years ago, I swore an oath to
support and defend the Constitution. Never did I dream that troops
taking that same oath would be ordered under any circumstance to
violate the Constitutional rights of their fellow citizens—much less to
provide a bizarre photo op for the elected commander-in-chief, with
military leadership standing alongside.

I am supposing that General Mattis is referring to the clearing of protestors so President Trump could safely visit St John’s Church that was set on fire the other night. First, President Trump said he had no knowledge of the clearing of protestors. He was not told. That was a decision by Bill Barr or someone concerned for his safety. If that had been President Obama would General Mattis or anyone else have had a problem with it? Trump did not ask anyone to violate the Constitution. Mattis likely penned his letter before he knew the facts. Also, what is bizarre about standing in front of a church in a show of support by the President of the United States. Nobody would have likely complained if it was a Mosque.

We must reject any thinking of our cities as a “battlespace” that
our uniformed military is called upon to “dominate.” At home, we
should use our military only when requested to do so, on very rare
occasions, by state governors. Militarizing our response, as we
witnessed in Washington, D.C., sets up a conflict—a false conflict—
between the military and civilian society. It erodes the moral ground
that ensures a trusted bond between men and women in uniform and
the society they are sworn to protect, and of which they themselves are
a part. Keeping public order rests with civilian state and local leaders
who best understand their communities and are answerable to them.

General Mattis, please see the history of the United States paying particular attention to the Civil War and Federal troops in Washington D.C. When civilian politicians are incapable or unwilling to protect the President military members are fulfilling their duty to protect the President.

James Madison wrote in Federalist 14 that “America united with
a handful of troops, or without a single soldier, exhibits a more
forbidding posture to foreign ambition than America disunited, with a
hundred thousand veterans ready for combat.” We do not need to
militarize our response to protests. We need to unite around a common
purpose. And it starts by guaranteeing that all of us are equal before
the law.

I have no disagreement with Madison’s philosophy. However, the conclusion of General Mattis is off the mark. Nobody is suggesting we need to militarize our response to protests. However, we may need to militarize our response to those throwing firebombs, shooting law enforcement, killing and beating innocent civilians, and vandalizing cities. Besides, the military is brought in to backfill for law enforcement just like they did under Obama for our Border Patrol. Lastly, if people were breaking into your home to set it on fire would you care who stopped the criminals? Would you honestly say, please burn my home? If a soldier tries to stop you I will stand against him?

Instructions given by the military departments to our troops
before the Normandy invasion reminded soldiers that “The Nazi
slogan for destroying us…was ‘Divide and Conquer.’ Our American
answer is ‘In Union there is Strength.’” We must summon that unity to
surmount this crisis—confident that we are better than our politics.

I’m not quite sure what the point is with this paragraph. I don’t see anyone suggesting that there is no strength in unity. However, we cannot unite with thugs. We did not unite with the Nazi’s. We can stand united with protestors and just as firmly against thugs.

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. We can unite
without him, drawing on the strengths inherent in our civil society.
This will not be easy, as the past few days have shown, but we owe it
to our fellow citizens; to past generations that bled to defend our
promise; and to our children.

I strain to keep my response to this brief. President Trump was not elected to unite us. His election was the result of a seriously divided country before his election. His battle cry from the beginning was “America First” in contrast to putting American citizens somewhere other than first. He is for all good and law-abiding American citizens. I agree there is a deliberate effort by President Trump to draw a division between the wrong-headed thinking of the Left and normal Americans. Even what was once a moderate Democrat Platform has morphed into a Socialist nightmare that seeks to remove the First and Second Amendments. I leave you with this thought on division. Even the Prince of Peace said this: “Do not suppose that I have come to bring peace to the earth. I did not come to bring peace, but a sword.” Matthew 10:34. In some respect, you have unwittingly likened President Trump to Jesus.

We can come through this trying time stronger, and with a
renewed sense of purpose and respect for one another. The pandemic
has shown us that it is not only our troops who are willing to offer the
ultimate sacrifice for the safety of the community. Americans in
hospitals, grocery stores, post offices, and elsewhere have put their
lives on the line in order to serve their fellow citizens and their
country…..

On this point, I and I suppose most of us wholeheartedly agree.

We know that we are better than the abuse of executive
authority that we witnessed in Lafayette Square. We must reject and
hold accountable those in office who would make a mockery of our
Constitution. At the same time, we must remember Lincoln’s “better
angels,” and listen to them, as we work to unite.

Only by adopting a new path—which means, in truth, returning to
the original path of our founding ideals—will we again be a country
admired and respected at home and abroad.

On the first part  “abuse of executive authority that we witnessed in Lafayette Square…. mockery of our Constitution.” see the answer to the second paragraph above.

The “better angels” that Lincoln referred to was during his first inaugural address. That was just before the war had started. “Lincoln denounced secession as anarchy, and explained that majority rule had to be balanced by constitutional restraints in the American system of republicanism.” Simply put the thing Lincoln fought against is the same thing Trump fights against. That thing is “anarchy”. The majority of Americans want law and order. They do not want their cities and neighborhoods burned.

As you say “Only by adopting a new path—which means, in truth, returning to the original path of our founding ideals—will we again be a country admired and respected at home and abroad.” is exactly what President Trump is trying to achieve. You may not like his style but the goal is the same. If you cannot see that, General Mattis, maybe you have spent too much time outside the United States.

In my lifetime (which is close to the same as yours General Mattis) nobody supports the Constitution like President Trump. Nobody has done more to bring accountability back to the Federal Government. I wonder if your reaction isn’t personal. After all, President Trump was right about Syria and you were wrong. I cannot help but wonder if that is what really sticks in your craw. Maybe you want a gig on MSNBC or CNN to go alongside the other disgraced former intel agency heads. I will not speculate any further. Just know that I and many other veterans are saddened by your attacks on our President.