In a serious breach of presidential norms, President Donald Trump urged sailors attending the commissioning of the USS Gerald R. Ford on Saturday to wade into the political fray and help lobby Congress on health care and other topics. “I don’t mind getting a little hand, so call that congressman and call that senator and make sure you get it,” Trump said of his budget, highlighting the defense spending portion. This could have been interpreted as an order from the commander in chief to the service members in attendance to support the Republican Party agenda. “And by the way, you can also call those senators to make sure you get health care,” he added.

That Trump would so command the troops—who he apparently sees as his troops—should come as no surprise. Time after time, he has breached long-standing norms of civil-military relations: from evading presidential responsibility, to appropriating service members’ valor for political purposes, to politicking before military audiences. Saturday’s breach stands apart because of its directness and its implications. Trump’s verbal command in Norfolk, Virginia, incites the assembled troops to discard centuries of U.S. military ethics and break long-standing military rules, too. This is what leaders do in banana republics: Instruct the people with guns to join the political fray.

The military tradition of avoiding domestic politics literally predates the country, going back to a dispute over veterans’ benefits between then-Gen. George Washington and his officers. The officers planned to confront Washington at Newburgh, New York, with a thinly veiled threat of military takeover if they didn’t get Washington’s support in a plea to Congress. Washington deftly defused the plot, telling his troops they would “sully the glory” they earned on the battlefield with their plans to lobby Congress.

In the two centuries since, the U.S. military has increasingly professionalized and bureaucratized itself. Today, the rules against troops’ political activity exist in the Uniform Code of Military Justice and several Pentagon regulations. Article 88 of the military justice code makes it a crime for an officer to use “contemptuous words” against the president, vice president, Congress, or certain other officials, whether for political purposes or not. Military Rule of Evidence 508 gives service members an absolute right “to refuse to disclose the tenor of the person’s vote at a political election conducted by secret ballot.”

In addition to these parts of the military’s criminal code, numerous Pentagon rules and regulations aim to keep service members out of politics. DoD Directive 1344.10 bars active and reserve service members from conducting political activity in uniform or in ways that suggest they carry the military’s imprimatur. Other DoD rules limit the way troops can wear their uniforms, use their titles, or express themselves on political issues too.

President Trump’s comments on Saturday inject legal risk and uncertainty into this system of rules. On the one hand he—as commander in chief of the armed forces—can be seen as effectively giving an order to the troops that they must obey. As a legal matter, the president’s authority trumps the Department of Defense’s rules on political activity, if not the UCMJ’s criminal provisions, although the latter can be read to allow what Trump wants. If the troops obey Trump in this instance, however, they must essentially disobey their own regulations, not to mention service norms and values.

There is real danger in the troops actually following Trump’s guidance. Lobbying Congress and entering the political fray can only be a distraction from defending the nation—a point subtly made by retired Maj. Gen. Charlie Dunlap in his brilliant essay “The Origins of the American Military Coup of 2012” nearly 25 years ago. Our military today enjoys the highest approval rating of any institution in society, but sullying itself with the mud of political debates can only harm that reputation.

More broadly, Trump’s commands inject uncertainty and doubt into the military, which depends on order and discipline for cohesion and effectiveness and combat. Which rules, exactly, are troops to follow when the president himself casts such doubt as he did in Norfolk? If the president believes the rules governing political activity don’t suit him, how broadly will that apply? Are they now allowed to fly “Make America Great Again” or “Trump for President” flags from their personal cars on base? From military vehicles? (This presumably would be a unilateral allowance, and expressing support for Democrats would still be verboten.)

If Trump someday wants to upend other inconvenient regulations, like the military’s rules on torture and interrogation, can he do so with a mere suggestion like this? Georgetown law professor and my colleague Rosa Brooks rightly pointed out how unlikely it was that the military would disobey a presidential order. The greatest danger of all posed by Trump’s disregard for military values is that he will someday go further than he did this weekend and undermine rules or norms with far graver consequences.

We often take civil-military relations for granted in this country because we have it so good. The greatest civil-military eruptions in recent history involve things like then-Gen. Eric Shinseki’s sobering 2003 testimony contradicting George W. Bush’s White House, saying that it would take “several hundred thousand” troops to pacify Iraq, or impolitic comments by Gen. Stan McChrystal’s staff in a 2010 Rolling Stone article. These skirmishes stand in stark contrast to the civil-military brawls in countries like North Korea—where the dear leader regularly executes top generals—or Pakistan, where the military dominates politics and has on occasion overthrown the government. American civil-military relations even look tame next to those in France, where newly elected President Emmanuel Macron just fired his top general, reminding his remaining brass that “I am your boss.”

Our civil-military relations are fragile and are already being strained by the Trump presidency. In just six months, he has given hyperpolitical speeches to military and intelligence audiences, used the Pentagon’s Hall of Heroes to sign his controversial first travel ban, and whined about how tough he had it in his speech at the U.S. Coast Guard Academy graduation. Trump’s top lieutenants have also aided this corruption of the civil-military ethic. Vice President Mike Pence misstated the rule on obeying orders in his graduation speech—omitting the important exception for unlawful orders. The national security adviser, Army Lt. Gen. H.R. McMaster, has debased himself and the military ethic, too, by leaping to Trump’s political defense after Trump gave highly classified information to the Russians, and then did so again in a vapid Wall Street Journal op-ed defending Trump’s “America First” agenda.

If left unchecked, Trump and his team will likely continue to tear the fabric of American civil-military relations, leaving tattered shreds of the military’s ethics and values in their wake. That is, unless three groups step up to play their constitutional role in checking Trump.

First, Congress must police Trump’s excesses through aggressive oversight. In confirmation hearings, Senate committees should continue to demand that senior Pentagon civilian and military appointees testify candidly back to Congress when called upon to share their views. Congressional oversight committees should regularly call military witnesses to testify, and use their hearings to solicit views from America’s career military leadership about the wisdom and efficacy of the Trump administration’s military policies as has been historic practice.

Second, military leaders must assert their professional norms and ethics more forcefully. Such dissent should occur in private first to respect the chain of command. Gen. Joseph Dunford, the chairman of the Joint Chiefs of Staff, has a statutory duty to serve as “the principal military adviser to the President.” In that role, he must raise his voice in defense of long-standing military norms and ethics when they are threatened by the president in ways that ultimately threaten the country. Likewise, senior military leaders should candidly and publicly answer congressional inquiries about strategy, policy, and resources—even where doing so exposes rifts with the White House—to enable Congress to play its constitutional role in national security affairs.

Finally, Trump’s own inner circle must do more to restrain the rhetorical excesses and explosions that have so far defined this presidency. This includes the generals he has tapped to serve in his Cabinet—McMaster, Secretary of Defense James Mattis, and Secretary of Homeland Security John Kelly—who must now teach their principal why these long-standing rules matter both for the country and Trump’s interests. Our country cannot take its healthy civil-military relations for granted nor expect these norms to survive too many more barrages from the current president. It remains to be seen whether Trump will accept such tutoring—or fire the teachers—but these active and retired generals owe it to the country to do their best to keep the president from running the ship of state aground.