Last May, I gave a lecture at the Air War College, the Air Force’s senior service school for officers. I have taught at West Point and spoken at several other senior service schools. At the Air War College, I presented my work on the history of U.S. civil-military relations—research that later led to a book that was favorably reviewed by The Wall Street Journal and the military’s Joint Force Quarterly. The college was complimentary of my presentation and invited me to reprise my talk this school year. But last week, I was asked not to come after all.The professor who gave me the news was polite and professional, apologetic even. In a statement to The Atlantic, a spokesperson for Air University, the college’s parent institution, said, “Air University adjusted its academic schedule following the recent government shutdown, including the Air War College program, to prioritize core curriculum and program requirements. As a result, the scheduled guest lecture by Dr. Kori Schake was unable to be accommodated within the revised schedule. This was a command decision.”Although I have no evidence that the decision was political, I nonetheless found myself wondering if something else was going on. The Defense Department under Secretary Pete Hegseth has made clear that people and institutions may be excluded from involvement in professional military education for ideological reasons. The Pentagon has cut academic ties with numerous elite colleges that Hegseth called “factories of anti-American resentment and military disdain,” and rescinded a former Biden-administration official’s professorial appointment at West Point. The department has also sought to control the ideas taught at military institutions, instructing the service academies to remove library books that promote “divisive concepts and gender ideology” and requiring them to cancel some classes because of their content.[Read: Holy warrior]Hegseth has created a command climate in which subordinates might fear defending their educational programs. The dynamic reminds me of the tightening of the rules of engagement in Afghanistan during the Obama administration: When the military command sets a new standard that subordinates are worried about violating, they sometimes comply preemptively and even more stringently than the formal directive might require.At any rate, the history of civil-military relations, the subject I was to lecture on, is extremely relevant today. Far more than their predecessors, Hegseth and President Trump have traduced the once-firm line between politics and the military. Here is what I would have said in my lecture.It was not inevitable that a military strong enough to defend U.S. interests could avoid state capture or resist a military coup—it wasn’t even likely. In fact, no subject worried America’s Founding Fathers more than the risk of a standing army threatening civilian governance. Complaints about the potential danger posed by military forces are prominent in the Declaration of Independence. Thirteen of the 85 Federalist Papers directly address the issue. The Constitution would not have been ratified without the Second and Third Amendments’ protections against the federal government’s use of military force. Beginning with the 1795 Calling Forth Act and in subsequent legislation, Congress restrained the chief executive’s ability to mobilize militia. The Founders would be astonished to see how massive the country’s defense establishment has become today, and even more surprised by its tradition of deference to civilian authority.How a country founded in fear of a standing army came to think of its military as a bulwark of American democracy is the subject of my work. As with so many other good things in American governance, George Washington’s example was crucial. While commander in chief of the Continental Army, Washington didn’t make demands of Congress; he pleaded and entreated, consistently reinforcing the war powers of the civilian authorities. Although he preferred a strategy of decisive battle, he adopted a “war of posts” because it was the best his army could carry out with the resources that Congress had provided. When Alexander Hamilton argued that the army should intimidate Congress into giving itself revenue-raising powers, Washington cautioned that an army “is a dangerous instrument to play with.” At the end of the war, Washington publicly surrendered his commission to Congress, “bidding an affectionate farewell to this august body, under whose orders I have so long acted.” Washington’s adroit handling of the 1794 Whiskey Rebellion as president established that a democratic government could legitimately compel compliance with the law, including by using the military. His unfailing commitment to civilian authority gave time for government institutions to sink roots, and established norms that gelled into the professional ethos of our military today.Those norms weren’t uniformly respected by either civilian or military leaders during the 18th and 19th centuries. The first American president to vet military officers by their political affiliation was Thomas Jefferson. Andrew Jackson, Zachary Taylor, John Fremont (twice!), William Tecumseh Sherman, Ulysses Grant, George Armstrong Custer, and other military officers exceeded their orders in ways that created severe political problems for the presidents they served. But they are all examples of singular leaders taking initiative in the conduct of their military duties, not of the gathering of armies to threaten the government.The most difficult civil-military case to assess is that of Grant. During the constitutional crisis of 1867–68, President Andrew Johnson fired the secretary of war and attempted to appoint Grant in his place while Grant was also serving as commander of the U.S. Army. When Congress threatened Grant with five years in prison and a $10,000 fine if he accepted the dual appointment, Johnson offered to do the time and pay the fine should Grant uphold the president’s authority. Grant was thrust into the most consequential civil-military test that any American officer has had to navigate, namely deciding which of the two constitutionally authorized sources of civilian control to obey—Congress or the executive. Grant chose to obey the law, not the commander in chief, establishing that in peacetime, congressional authority takes precedence.In the 1870s, political jockeying led to what would become the nation’s most important restriction on the use of military forces domestically, the Posse Comitatus Act. For more than a decade after the Civil War ended, formerly seceded states remained under military occupation. Violence was so prevalent that, in 1871, Grant invoked martial law in South Carolina. He sent federal troops to protect legislatures and polling places, and even to supervise the counting of ballots in Louisiana, South Carolina, and Florida during the 1876 presidential election. By that time, however, support for Reconstruction had waned. Rutherford B. Hayes, the Republican presidential nominee, made a pledge to end it in exchange for the southern states’ votes, and won. Congress enacted the bargain in 1878 by prohibiting, via Posse Comitatus, the use of U.S. military forces for law enforcement unless Congress authorizes such action, it is requested by a governor, or the president invokes the Insurrection Act. (Just last year, in Trump vs. Illinois, the Supreme Court reinforced this restriction.) Presidents can also override Posse Comitatus to ensure that states respect constitutional rights. Dwight Eisenhower did this in 1957 by federalizing the Arkansas National Guard and sending active-duty troops to the state—over the governor’s objection—to enforce the Court’s Brown v. Board of Education ruling.In the 20th century, even as the size of the U.S. military ballooned, fewer military leaders challenged civilian authority than had in the prior century. There are only two examples of consequence: During World War I, Admiral William Sims expressly violated President Woodrow Wilson’s order that U.S. forces would be associated but not integrated with those of allies, and during the Korean War, General Douglas MacArthur publicly campaigned against President Harry Truman’s strategy for the war. In both cases, the civilian leaders easily prevailed. In the 1930s, the Marine Corps, the most independent of the military services, wrote a doctrine explicitly subordinating its expeditionary forces to the direction of diplomats. There were no significant civil-military disputes during World War II despite the military’s preference, contra the civilian leadership, for an Asia-first strategy. A 1949 dispute over government funding for the military was branded as the “revolt of the admirals” but was in fact a legitimate public debate about postwar budgets and strategy, not a refusal by the military to enact them.[Read: What Anthropic’s clash with the Pentagon is really about]In more recent times, civil-military frictions have consisted almost entirely of civilian leaders pushing the military up to or over the bounds of traditional decorum or even the law. Most dangerously, Trump has deployed military forces into cities and states over the objections of their mayors and governors, or has attempted to. The abrupt retirement last year of the head of the U.S. Southern Command amid a series of controversial U.S. boat strikes in the Caribbean, along with the fact that a classified Justice Department memo reportedly indemnified the military against prosecution for the strikes, suggests at least some level of concern inside the government that the administration is operating very close to the legal line in those operations.More commonly, politicians today attempt to legitimate their policies and themselves by using the military as a prop: Think of candidates flaunting endorsements from veterans, and political conventions showcasing them as speakers. President Biden had uniformed Marines standing behind him when he gave a 2022 speech about democracy. Trump has given campaign speeches to military audiences and encouraged their participation in partisan activities. In a recent video, several Democratic members of Congress reminded the military not to obey illegal orders, making compliance with the law seem like a political act. Veteran endorsements appear to have a small-to-negligible effect on voters, but may also negatively affect their attitudes about the military as an institution.The military’s ability to resist politicization rests almost wholly on the professionalism of the force itself. When Hegseth called hundreds of military leaders to Quantico, Virginia, last fall to watch what turned out to be political-rally-style speeches by him and Trump, the military leaders showed up, as they had been directed to do by their civilian leaders. But they all sat in stoic silence during the political program. This kind of professionalism runs deep in the U.S. military. Yet the armed forces will not long remain immune to our febrile politics if we keep dragging them into it. Avoiding that will be even harder if service members are denied opportunities to learn the history of the military’s relationship with its civilian leaders.