The military establishment’s anger at President Trump’s politicization of the armed forces has been building for three years. It finally ripped open in the aftermath of Monday’s appalling presidential photo op at St. John’s Episcopal Church.

The break was a decisive moment in the Trump presidency. But such inflection points are mysterious. Why does a bridge that has carried a million vehicles suddenly collapse when one more heavy load rumbles across? It’s not a linear process but a sudden discontinuity. Mathematicians call it “catastrophe theory.”

The catastrophe Monday was that Trump was advocating what military officers dread most. He was preparing to mobilize the armed forces to suppress protests by U.S. citizens against racial injustice and police brutality. For military officers who have sworn an oath to defend the Constitution, this was overload. The structure cracked.

The most dramatic break came from retired Gen. Jim Mattis. For the 18 months since his resignation as defense secretary in December 2018, Mattis had been asserting a “duty of silence” as a former military commander not to directly criticize the president. Many had pressed Mattis to speak out, but he had been adamant.

This bridge of silence toppled Wednesday, when Mattis released a statement expressing the rage he has long felt as he watched Trump demean the military and its professionalism. Mattis wrote for the history books: “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.”

The stage for Mattis’s excoriation was set by several prior events that are crucial in understanding Monday’s inflection point. The first was an opinion piece published in the Atlantic on Tuesday afternoon by retired Adm. Mike Mullen, former chairman of the joint chiefs. Mullen, like Mattis, had been reluctant to use his military credentials to challenge Trump.

But Mullen had reached his choke point. His piece, titled “I Cannot Remain Silent,” challenged Trump’s consideration of using active-duty troops to put down the protesters: “I am deeply worried that as they execute their orders, the members of our military will be co-opted for political purposes.” Mullen also condemned “police brutality and sustained injustices against the African American community.”

Mullen had put down a marker. Many former colleagues of Mattis wondered why he had not already made a statement like Mullen’s. When Mattis’s blistering message eventually came, it was worth the wait.

This drama has a final, largely invisible, chapter that involves Gen. Mark A. Milley, chairman of the Joint Chiefs of Staff, and Mark T. Esper, the defense secretary. They accompanied Trump on that walk across Lafayette Square, Milley in uniform. It was a decision they would both deeply regret.

Milley had been telling the president since late last week that it would be a mistake to invoke the Insurrection Act of 1807 and call out active-duty troops. Yet Trump told governors Monday that he was putting Milley “in charge” of a military response. The argument came to a head in the Oval Office that day, before the walk across Lafayette Square.

A burly man whose temper can match Trump’s, Milley was vocal in reiterating his advice to the president against mobilizing troops, according to three knowledgeable sources who spoke on condition of anonymity. Mullen and Mattis knew that Milley had taken this precarious position when they spoke out publicly, in part to support his effort to resist calling up the military. Trump hasn’t yet invoked the Insurrection Act, perhaps because he has weighed the private caution from his chief military adviser.

Milley, dressed in the baggy camouflage uniform that commanders wear in war zones, briefly wandered the streets after the church incident. It was the wrong image, but he expressed the correct sentiment the next day in a message to troops around the world: “As members of the Joint Force — comprised of all races, colors, and creeds — you embody the ideals of our Constitution.”

Esper has been walking a political tightrope, trying to support Milley without contradicting the president. That awkward two-step hasn’t worked very well, with Esper seeming to disagree with the president when he talked to the media Tuesday night and Wednesday, and then challenging reports that his views were any different from Trump’s. Like others who seek to remain in Trump’s good graces, Esper seemed to be playing both sides.

It was Esper who unintentionally offered an epitaph for this hinge moment in U.S. history. Of his walk to the church, Esper said, “I didn’t know where I was going.” Whatever he intended, Esper was allowing the armed forces to be manipulated as a political prop. The military fought back hard — and correctly — against this abuse.

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