Military and intelligence personnel have an affirmative obligation to disobey manifestly illegal orders. But when a group of Democratic lawmakers, all of whom are veterans or former intelligence officers, released a video reminding their former colleagues of this obligation, President Donald Trump accused them of sedition and threatened them with death. The Pentagon has now announced that it is investigating one of those Democrats, Senator Mark Kelly, and could even court-martial him.

Though they weren’t explicit, the Congress members seem likely to have been speaking about Trump’s assault on the Venezuelan cartels. Are those assaults legal? A memo from the Justice Department argues yes on the legal grounds that the United States is in an armed conflict with the cartels. The memo, drafted by the Office of Legal Counsel and reported on by The New York Times, goes on to assure military members that they can rely on the OLC’s legal conclusions and that they will be immune from prosecution if they follow the president’s orders. In most cases, that would be enough: A lawyer’s advice that an act is lawful can typically be used as a basis for arguing that someone did not think she was acting illegally. But in this case, the protective value of the OLC opinion may be no greater than the value of the paper it is written on.

Part of being a lawyer is giving formal legal opinions to one’s clients. These opinions are intended to provide clarity as to a client’s legal obligations in uncertain situations. Thus, clients often seek out such opinions in an effort to cover themselves down the road. If their actions are later questioned, they can say that they sought and followed the advice of an attorney. Doing so is not a bulletproof defense—their attorney may, after all, have been wrong. But it does offer powerful evidence that any violation of the law was not intentional.

[Listen: Would U.S. generals obey illegal Trump orders?]

Except, of course, if opinions are based on false factual premises; these typically carry no weight in court. The OLC memo may be just such an opinion, as it seems to be based on fraudulent claims about the nature of drug trafficking from Venezuela. Military officers who rely on an opinion that they reasonably should know is premised on a false set of claims do so at their own peril.

According to The New York Times, the memo is “said to open with a lengthy recitation of claims submitted by the White House, including that drug cartels are intentionally trying to kill Americans and destabilize the Western Hemisphere,” and that, therefore, the cartels’ ships are a legitimate military target. The memo then argues that the cartels’ boats are lawful military targets because the narcotics on them are going to be sold for money that will be spent on military equipment—again, for the purpose of killing their American customers.

As support for the claim that the cartels intend to kill Americans, the memo relies on the assertion that the cartels are responsible for the deaths of tens of thousands of Americans a year. That might be a reference to the fentanyl trade; but fentanyl comes from labs in Mexico controlled by Mexican cartels, and the memo never makes a factual connection between those cartels and the South American groups whose boats are being destroyed. Nor does the memo ever declare, as least as far as is publicly known, that deaths from the cocaine that is purportedly on the targeted boats, and that is responsible for significantly fewer deaths annually in the U.S. than fentanyl, would justify the designation as a foreign terrorist organization. Also unclear is how boats in the Pacific (whose attack the memo is also said to authorize) might be in any way connected to South American cartels operating from a country with no Pacific coast.

The OLC opinion apparently is grounded in factual assertions that are not only in error but are widely known to be wrong—both by the general public and, more importantly, by the military officers whom it purports to protect.

[Paul Rosenzweig: State of permanent fake emergency]

The memo takes the unusual step of including a section identifying potential legal defenses if a prosecutor were ever to charge troops for crimes related to the killings—an implicit admission that the OLC knows the weakness of its views. They’re so weak in fact that, if public reports are to be credited, a number of senior national-security lawyers who doubted the memo’s conclusions have been fired or reassigned. In that sense, the assurance itself has a perverse effect: It serves only to emphasize that the OLC knows it is in legally treacherous waters.

If military personnel who are participating in the extrajudicial killing of foreign nationals are ever charged with violations of U.S. or international law, they will presumably argue that they were merely following orders and had relied on advice from the lawyers. But given the flimsy nature of the OLC’s opinion, the orders they have received seem quite possibly unlawful. If they are, a prosecution could be brought against any individual (and most especially general officers) who purported to rely on this opinion to justify their actions if it can be proved that they knew or reasonably should have known that the factual assumptions of the opinion were false. And some in the military clearly do know about the problem. According to The Washington Post, an unknown number of junior officers “fearing potential legal exposure, asked military lawyers, known as judge advocates general, for written sign-off before taking part in strikes.” They didn’t get that reassurance.

Whether the next administration will want to bring these cases is a different question, but officers who are relying on Trump’s opinion are risking a great deal on a foundation of sand. Factually bankrupt opinions don’t make unlawful orders lawful.