Only one of these men is in the military chain of command. Photo: Chip Somodevilla/Getty Images

The first casualty of President Trump’s deployment of active-duty troops to our southern border — or maybe the second, if you count the line between military policy and naked partisanship as the first — has been clarity. Over the last ten days, we’ve had reports that troops were finishing their mission and leaving the border, and then reports that they weren’t. The administration changed the rules to limit where would-be refugees could apply for asylum, until a court said it couldn’t.

Now there’s been another bewildering development. According to Military Times’ Tara Copp, a memo came down from the White House on Tuesday evening authorizing active-duty troops at the border to fulfill some functions of law enforcement for the “protection of border agents” — including searching and detaining people, crowd control, and “lethal force, where necessary.”

National security lawyers all over the country lifted their heads from their Thanksgiving preparations in alarm. It has been very settled law for more than a century that active-duty troops may not be used for law enforcement functions within U.S. borders. That law, the Posse Comitatus Act, was passed just after the Civil War and Reconstruction, specifically to protect state governments from having policies they didn’t like enforced by federal military personnel on their soil. The exceptions are extreme: the president can “use military force to suppress insurrection or enforce federal authority,” per the Congressional Research Service. It’s worth noting that service members always have the right to use force for self-defense — but the idea is that troops are not to be used in roles where they might choose to use force for other reasons.

There are several strange things about this document that immediately jump out. It was called a “Cabinet order,” but the Cabinet has no constitutional authority to make orders, and certainly not of the military. Sometimes in past administrations, the White House has sent “Cabinet memos” — but those merely enumerated explicit presidential guidance. This memo, instead of invoking the president’s authority, was signed by Chief of Staff John Kelly — but chiefs of staff have no authority to command anyone except White House employees. (And in my experience from the Clinton White House, that’s certainly not a group you would want to put in charge of crowd control.) The fact that Kelly is a retired four-star general is irrelevant; no chief of staff fits anywhere in the military chain of command.

Legal and defense experts on Twitter came up with several theories as to why Kelly might have signed the document. National security lawyer and Hill veteran Mieke Eoyang wondered whether the relevant legal advisers had refused to sign off on such an order. Former Pentagon senior official Brian McKeon theorized that the document was a deliberate ploy by Kelly, to mislead Trump into thinking that he had ordered that lethal force be used without the Pentagon ever executing the move. Lawfare editor Scott Anderson asked whether Trump might be protecting himself by having Kelly sign — because violations of the Posse Comitatus Act can carry criminal penalties.

This might be a bit funny — another crazy Trump spectacle — except that it concerns the president’s most solemn responsibility, and thus threatens to put the world’s strongest fighting force crossways of our democratic practices.

Veterans’ groups have said all the way along that the deployment of roughly 5,900 troops to the border enmeshes them in American politics and is a waste of their training and skills. Now we’re in a situation where some authority figures seem to be saying troops can act as law enforcement officers, while others disagree. Secretary Mattis took time with a press gaggle Wednesday afternoon to stress that the military would not violate the Posse Comitatus Act. “I have the authority,” Mattis said when asked about the Cabinet order, noting that pictures of troops at the border show they’re unarmed. “Relax. Don’t worry about it.” Nevertheless, this is still a recipe for confusion, and potentially for tragedy — what happens if stressful, chaotic situations arise on the border, like demonstrations?

Lawyers had another concern: was the White House asserting its right to skip legal review or, even more broadly, was it saying that the president’s responsibility to defend the country allows him to ignore laws he doesn’t like? That’s a precedent that could affect lives and freedoms all across the country, and far from the border, from surveillance to search to immigration and more.

It’s worth noting that there are American clergy, activists, and media traveling with the Central American migrants. It’s very likely that, in the case of a confrontation at or near the border, U.S. troops would be pointing their weapons at U.S. citizens. The idea that you could use Americans who swore an oath to defend their country to attack and kill other Americans whose political views you don’t like is the very thing the Posse Comitatus Act was intended to protect us from. Members of Congress from both parties should be speaking up to demand clarification.