One of the most interesting aspects of these documents, however, is what was left out of them. Last Friday, the Associated Press reported on a leaked draft of one of the memos. The draft directed the federal government to enter into agreements with 11 states authorizing National Guard troops to round up and detain undocumented immigrants living inside the United States.

Confronted with the memo, White House press secretary Sean Spicer issued his now-familiar boilerplate denial, calling the AP story “false” and declaring that the memo “is not a White House document.” A Department of Homeland Security spokesperson, however, confirmed that the memo was an early draft, albeit one that had never been seriously considered. Meanwhile, agency employees told reporters it was under active consideration as of February 10.

Based on the final version of the memorandum released Tuesday, it appears that the idea was indeed rejected…for now. But it would be a mistake to ignore it. The draft memo provides a sobering window into how an administration that seems bent on expanding executive power views the proper role of the military—an issue that may well arise again.

The role of the military in law enforcement
What the draft memo proposed would have been unprecedented. Between 2006 and 2008, President Bush sent National Guard troops to assist in border security; in 2010, President Obama did the same. In both cases, though, the troops served in a support role, providing assistance with tasks like building fences, conducting aerial surveillance, and manning observation posts. They did not directly engage in the core law enforcement functions of arrest and detention.

The presumption against military forces taking on the work of local and state police and law enforcement is encoded in our national DNA. Based on their experience under English rule, the founding fathers believed that standing armies could easily become agents of tyranny. The framers of the Constitution were thus careful to keep the army under civilian control, and to divide military authorities between the president and Congress. The Constitution contains only one explicit allowance for domestic deployment of the military by the federal government: It authorizes Congress—not the president—“[t]o provide for calling forth the militia to execute the laws of the union, suppress insurrections and repel invasions.”

Congress has passed a handful of statutes delegating this authority to the president when specific criteria are met. For the most part, those criteria involve situations of clear emergency, where local police and authorities have been overwhelmed—or have themselves rebelled. Congress also passed the Posse Comitatus Act in 1878, making it a crime for federal troops to assume policing and law enforcement functions not expressly authorized by statute or the Constitution.

The National Guard and the Title 32 loophole
The draft memo, however, proposed the use of the National Guard, which occupies a unique status in the military. National Guard units can be “federalized” and serve as a part of U.S. armed forces; they can operate as state militias under the governors’ command; or they can operate in a hybrid status, carrying out federal missions using federal funds but remaining under local control.

When operating in the federal service (known as “Title 10 duty status”), the National Guard is subject to the Posse Comitatus Act, and may perform only those law enforcement duties expressly authorized in federal law. Their law enforcement powers are thus largely limited to emergency situations such as insurrection, domestic violence, riots, or natural disasters.

When operating as state militias (i.e., in “state active duty” status), National Guard units are not subject to the Posse Comitatus Act; they are governed instead by state law. The laws of some states are quite permissive, allowing units to assume a law enforcement role in a wide range of circumstances. Others, however, allow deployment only in emergencies. Moreover, states receive no federal funds for activities undertaken in “state active duty” status, which no doubt limits their enthusiasm for conducting federal law enforcement in that mode.

Enter the hybrid construct known as “Title 32 duty status.” In this role, National Guard units serve a federal purpose, comply with federal standards, and receive federal pay and benefits. But command and control remain with the governor—a legal nicety that allows the federal government to use the militias while avoiding the constraints of the Posse Comitatus Act.

What are the limits?
Federal law authorizes National Guard units to engage in three types of activity when in Title 32 status. First, they may conduct certain drug interdiction and counter-drug activities. Second, the secretary of defense may commission them to perform a “homeland defense activity” to protect territory or populations from “a threat or aggression against the United States.” Third, they may be required to participate in training, drills, and field exercises to ensure their readiness for federal service.

At first glance, these seem like fairly narrow authorizations. Tucked into the provision on drills and field exercises, however, is language stating that Guard members may be ordered to perform additional “training or other duty,” which may include “[s]upport of operations or missions undertaken by the member’s unit at the request of the President or Secretary of Defense.” Read literally, this would allow National Guard troops to undertake any assignment—including any federal law enforcement activity.

It seems unlikely that Congress buried a blanket authorization in one of three carefully limited sets of authorized activities. A more sensible reading is that the duties, operations, or missions referenced in the training provision are those stemming from other specific grants of authority in the law. Nonetheless, this language has been invoked to provide federal pay for troops who provided airport security after 9/11 and undertook disaster relief missions after hurricanes Katrina and Rita.

Using Title 32 to conduct immigration enforcement would have upped the ante. The attacks of 9/11, Hurricane Katrina, and Hurricane Rita were isolated disasters requiring an urgent response, and the bulk of the National Guard’s activities fell outside core law enforcement functions. If Guard members were to take on the day-to-day enforcement of federal immigration law, it would fundamentally change the relationship our country has with its military.

Looking forward
For now, we appear to have dodged that bullet. But that is no cause for complacency. President Trump never elaborated on his January tweet threatening to “send in the Feds” if Chicago did not bring down its crime rate, but the warning takes on a more alarming cast in light of the draft memo. Nor is it hard to imagine Trump deciding to task the National Guard with enforcing domestic counterterrorism laws.

That is a bridge our country simply should not cross. In free democracies, soldiers do not knock on doors, arrest people, and imprison them as a matter of routine—no matter what law they are suspected of violating. Our founding fathers understood this intrinsically. The latest leaked memo should serve as an early warning that our new president might not.

Liza Goitein is co-director of the Liberty & National Security Program at the Brennan Center for Justice.