Our security is dependent on those who are willing to fight our foreign enemies and die for their country. We honor them and their families because their bravery and courage protect our democracy. We respect our military precisely because its role in defending the nation means that the military does not get involved in politics. If we allow the president to politicize the military, that will undermine the trust of the American people in our national security. The mobilization of the National Guard in California has raised concerns about whether the reason for its deployment was based on real threats to law and order, or on political differences between the governor of California and the president of the United States.

To protect the role of the military, the U.S. has historically made clear in its laws that federal troops should not be used for civilian law enforcement. In 1878, President Rutherford Hayes signed the Posse Comitatus Act, which bars the military from doing the work of law-enforcement officers. Even the statutes that authorize the president to activate the National Guard make clear that troops are to be limited to responding to “invasions” or “rebellions.” The U.S. is not facing either an invasion or a rebellion.

Respect for the military’s role is crucial for our democracy. That is why the law is designed to ensure that our armed forces are not politicized or misused. This rule-of-law tenet is the fundamental difference between a free society and an autocracy. Tyrants use the military as a pawn to solidify power, put down protests, and arrest opponents. Russian President Vladimir Putin has incurred as many as a million casualties among the soldiers he sent into Ukraine for his dictatorial goal of restoring the supposed greatness of the Soviet Union. Putin has found an ally in another ruthless autocrat, North Korea’s leader, Kim Jong Un, who has sent forces to help Russia’s fight in Ukraine. In China, the primary purpose of the military is to protect those in power. In each case, the tyrant demands—for his own survival—that the loyalty of the military is solely to him, not to the nation, let alone the people.

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Doing a dictator’s bidding is not how the military works in America. Our service members swear an oath of loyalty to the Constitution, not to the president. They follow the orders of the president as their commander in chief, but may do so only if those orders are legal and pursuant to the Constitution. Their job demands training, skill, and courage, certainly. The job also requires the capacity to make decisions based solely on the goal of accomplishing a national-security mission, not appeasing political leaders. As secretary of defense, I was a party to the kinds of tough decisions our military has to make. That judgment must not be damaged by those who seek to use it for political purposes.

At the Pentagon, I bore the vital responsibility of deciding on the deployment of our men and women in uniform, and whether to put them in harm’s way. The concern that some of those deployed would not return from a mission was always uppermost in my mind. Whenever we lost a serving soldier, I would receive a report and see their name. On those occasions, I personally wrote a condolence note to their family. The list of fallen warriors was also sent to the White House so that the president could do the same and convey the nation’s gratitude to the family for the sacrifice that their loved one had made.

Admiral Bill McRaven, the head of Special Operations Command at the time, made clear to me that every military judgment must be based on doing what’s right to accomplish the mission. As the director of the CIA, I was in charge of the covert operation to hunt down the al-Qaeda leader Osama bin Laden at his secret compound in Abbottabad, Pakistan. McRaven was the Afghanistan-based operational commander of the raid, in which two teams of Navy SEALs flew 150 miles at night. As they were about to land, residual heat from the day caused one of their helicopters to stall out and make a hard landing that left its tail stuck on one of the compound’s walls. I called McRaven to ask what was going on. He was decisive in his response. “I have called in a backup helicopter, and we will proceed with the mission breaching through the walls,” he said. “The mission will go on.” I gave my approval. The mission was successful: The man who had masterminded the 9/11 attacks was finally eliminated. The kind of split-second judgment that McRaven showed is what our military is trained to do.

In the recent success of the U.S. forces that were deployed to attack Iran’s nuclear facilities, the military did a great job of planning and execution. America has the strongest military force on Earth, but all of the technologically advanced weapons, planes, ships, and equipment would not be worth much without the skill and training of our service men and women. At outposts throughout the world, they are our front line of defense. They are our national security.

To maintain that security demands that we protect and respect the constitutional purpose they serve. If a president deliberately misuses the military for partisan reasons, he is weakening America’s safety. Leadership of a military devoted to defending our nation is an honored role that goes back to George Washington and the creation of the Continental Army 250 years ago. During that long history, Americans have learned that presidential parades do not define their military; what does is their respect for the military’s mission of protecting national security. Trust in the military is indivisible from trust in the Constitution. Both must remain inviolable.