The inquiry by the House’s Jan. 6 committee has produced many startling findings, but none to us more alarming than the fact that while rioters tried to thwart the peaceful transfer of power and ransacked the Capitol on Jan. 6, 2021, the president and commander in chief, Donald Trump, abdicated his duty to preserve, protect, and defend the Constitution.

In the weeks leading up to that terrible day, allies of Mr. Trump also urged him to hold on to power by unlawfully ordering the military to seize voting machines and supervise a do-over of the election. Such an illegal order would have imperiled a foundational precept of American democracy: civilian control of the military.

Americans may take it for granted, but the strength of our democracy rests upon the stability of this arrangement, which requires both civilian and military leaders to have confidence that they have the same goal of supporting and defending the Constitution.

We hope that the country will never face such a crisis again. But to safeguard our constitutional order, military leaders must be ready for similar situations in which the chain of command appears unclear or the legality of orders uncertain.

The relationship between America’s civilian leadership and its military is structured by an established chain of command: from unit leaders through various commanders and generals and up to the secretary of defense and the president. Civilian authorities have the constitutional and legal right and responsibility to decide whether to use military force. As military officers, we had the duty to provide candid, expert advice on how to use such force and then to obey all lawful orders, whether we agreed or not.

The events of Jan. 6 offer a demonstration on how military and civilian leaders execute this relationship and what happens when it comes under threat. When a mob attacked the Capitol, the commander in chief failed to act to restore order and even encouraged the rioters. As Gen. Mark Milley, chairman of the Joint Chiefs of Staff, testified to Congress, Vice President Mike Pence attempted to fill the void by calling on the National Guard to intervene.

Given the urgent need to secure the Capitol, Mr. Pence’s request was reasonable. Yet the vice president has no role in the chain of command unless specifically acting under the president’s authority because of illness or incapacitation, and therefore cannot lawfully issue orders to the military. Members of Congress, who also pleaded for military assistance as the mob laid siege to the Capitol, are in the same category. In the end, the National Guard deployed not in response to those pleas but under lawful orders issued by the acting secretary of defense, Christopher Miller.

Should civilians atop the chain of command again abandon their duties or attempt to abuse their authority, military ranks can and must respond in accordance with their oaths — without a lawful order from appropriate command authority, they cannot unilaterally undertake a mission. Concurrent with a duty to obey all lawful orders is a duty to question and disobey unlawful orders — those a person “of ordinary sense and understanding,” as a Court of Military Review ruling put it, would know to be wrong.

Operations on U.S. soil must also specifically comply with the Standing Rules for the Use of Force, which limit use of force but explicitly authorize it to protect people from imminent threat of death or serious harm, to defend “assets vital to national security” and “to prevent the sabotage of a national critical infrastructure.”

These are essential checks on civilian officials who would make unlawful use of U.S. military personnel. Governors, who possess broad command authority over our 54 National Guard organizations, for example, may face political pressure to deploy these forces to illegally interfere with elections or other democratic processes.

To recognize these threats to our democracy, military leaders must continue to develop robust training, guidance and resources for service members in accordance with these safeguards, ensuring the integrity of the chain of command and effective operation of civil-military relations.

But while such preparedness is necessary, it is not sufficient.

We each took an oath as former leaders of the armed forces to “support and defend the Constitution of the United States against all enemies, foreign and domestic.” We fulfilled that oath through service to civilian leadership elected by and accountable to the American people. This essential arrangement, however, is not self-executing; it relies on civilian leaders equally committed to protecting and defending the Constitution — including, most important, the commander in chief.

The principle of civilian control of the military predates the founding of the Republic. In 1775, George Washington was commissioned as the military commander of the Continental Army under the civilian command authority of the Second Continental Congress. The next year, among the grievances listed in the Declaration of Independence against King George III was his making “the military independent of and superior to the civil power.”

The president’s dereliction of duty on Jan. 6 tested the integrity of this historic principle as never before, endangering American lives and our democracy.

The lesson of that day is clear. Our democracy is not a given. To preserve it, Americans must demand nothing less from their leaders than an unassailable commitment to country over party — and to their oaths above all.

Source: Adm. Steve Abbot, Gen. Peter Chiarelli, Gen. John Jumper, Adm. James Loy, Adm. John Nathman, Adm. William Owens and Gen. Johnnie Wilson are retired four-star generals and admirals in the U.S. armed forces,