President Trump has seemed poised in recent days to present members of the armed services with a terrible choice: follow the commander in chief’s orders or abide by the law. After a U.S. drone strike killed Maj. Gen. Qasem Soleimani, an Iranian military leader who was a thorn in the side of multiple presidential administrations, Trump warned that he would respond to any counterattacks from Tehran by targeting Iranian cultural sites and striking back at Iran “perhaps in a disproportionate manner.”

These threats, if carried out, would involve blatant violations of the law of war, which prohibits attacks on culturally important sites and requires that force be used proportionately. Pressed on this Jan. 7, Trump was coy: “I like to obey the law. … But if Iran does anything they shouldn’t be doing, they’re going to be suffering the consequences, and very strongly.”

Service members have a legal duty to obey orders from their superiors, all the way up the chain to the president. But military personnel also swear an oath to the U.S. Constitution and are obligated to comply with the law of the land. When an order conflicts with a clear legal requirement, the obligation to follow orders is superseded by the obligation to comply with the law. In fact, service members have a legal duty to refuse to obey manifestly unlawful orders, and those who follow unlawful orders can be prosecuted criminally. U.S. military court-martial rules reflect principles made famous by the Nuremberg tribunal: “I was just following orders” is no defense when “the accused knew the orders to be unlawful or a person of ordinary sense and understanding would have known the orders to be unlawful.”

In other words, military leaders — and, for that matter, lower-ranking service members — have only one legally permissible response if confronted with a presidentially initiated unlawful order: “No, sir.”

But in practice, it’s rarely so straightforward. When President George W. Bush decided to greenlight the waterboarding of terrorism suspects, for instance, he didn’t announce that he was ordering U.S. personnel to commit war crimes by violating legal prohibitions against torture. On the contrary, he continued to publicly insist that the U.S. abhorred torture — while finding ethically challenged Justice Department lawyers willing to ignore decades of settled law and argue that waterboarding wasn’t really torture. As a result, those involved in the Bush administration’s “enhanced interrogation” program faced a decision: defend long-standing legal and moral principles, thereby risking their careers, or accept the assurance of administration lawyers that waterboarding wasn’t really torture. Several senior military officials and JAGs registered dismay over the Bush administration’s legal reasoning, but almost no one disobeyed or resigned.

Trump’s recent tweets and comments have suggested an overt willingness to order military personnel to commit acts that would constitute war crimes. “If Iran strikes any Americans, or American assets, we have … targeted 52 Iranian sites (representing the 52 American hostages taken by Iran many years ago), some at a very high level & important to Iran & the Iranian culture, and those targets, and Iran itself, WILL BE HIT VERY FAST AND VERY HARD,” he tweeted Jan. 4. Reminded by reporters that this would be illegal, Trump doubled down: “[T]hey’re allowed to kill our people. … And we’re not allowed to touch their cultural site? It doesn’t work that way.” The next day, he added a new Twitter threat: “[S]hould Iran strike any U.S. person or target, the United States will quickly & fully strike back, & perhaps in a disproportionate manner.”

Trump’s contempt for the law is right out in the open. But Trump, like Bush, has tame lawyers at his disposal who stand ready to muddy the waters. If Trump decides at some point to follow through with his Twitter threats, expect his lawyers to argue that the targeted sites don’t really have cultural importance, or that every cultural site targeted was hiding nuclear weapons or sheltering terrorists. Expect to hear that the president’s use of the word “disproportionate” was a misstatement or a rhetorical flourish. Or perhaps they’ll go further, arguing, as Nixon famously did, that when the president breaks the law, “it’s not illegal.” After all, Trump’s lawyers have already argued — in court — that Trump is entirely immune from both investigation and prosecution.

Another problem for conscience-ridden service members is that Trump’s unlikely to look kindly upon those who refuse orders to break the law. In November, Trump personally intervened in several military cases to pardon service members accused or convicted of war crimes. In December, he proudly trotted out the men he pardoned at a fundraising event and hailed them as warriors and heroes — while the service members who turned them in and the Navy officials who sought to discipline them have been vilified as cowards and “snowflakes” on right-wing media. Trump appears to see war crimes as a sign of strength, and people who wring their hands about war crimes as weak and traitorous. The message to service members is clear: Those who commit war crimes will be praised and, if necessary, pardoned.

Given the circumstances, no one should expect to see large-scale military disobedience even to blatantly unlawful orders. When the commander in chief has made clear his disregard for basic legal principles, it would require unusual moral fortitude to disobey his commands.

Bush at least tried to cloak his administration’s use of torture in legal sophistry, a backhanded testament to the strength of the norms his aides sought to circumvent. (“Hypocrisy,” French moralist François de La Rochefoucauld once said, “is the homage vice pays to virtue.)” In contrast to Bush, Trump makes no secret of his disdain for the laws of war. Thus far, thankfully, he hasn’t acted on his Twitter threats. But when the president of the United States can’t even be bothered to pay lip service to principles of legality, the rule of law is already in serious trouble.