As America enters a presidential election year, the crisis at our southern border is an issue that continues to occupy a great deal of attention and concern. Republican candidates echo national sentiment that border security is a matter of national security and must be an administration’s priority. And despite relatively lax immigration enforcement during the majority of his term, even President Biden is now shifting his position as the election approaches.

Nevertheless, while commentators seem to tacitly acknowledge that President Biden must do something amid sharpening criticism, the knives are out against former President Trump and his campaign’s promises to use federal troops to enhance border security. Some even go so far as to liken Trump to a “dictator” and to declare his plan a violation of federal law.

These arguments invoke the Posse Comitatus Act, but this federal law, contrary to the dictator claims, does not prohibit a president from using federal military forces to secure our borders. Just as sitting presidents have the authority to declare a state of national emergency, they also have the authority to deploy troops to secure our borders under certain circumstances.  

The Posse Comitatus Act, codified at 18 U.S. Code, Section 1385, was first passed in 1878 to resolve concerns that the federal military was being used to enforce domestic laws in former Confederate states. Under its original terms, the Posse Comitatus Act prohibited the use of the Army as a posse comitatus (which means domestic law enforcement) “except in cases and under circumstances expressly authorized by the Constitution or Act of Congress.”

After World War II, Congress included the Air Force as subject to the Act, but strangely it did not include the Navy or Marine Corps, although a subsequent Department of Defense Regulation applies it to them. However, as a maritime law enforcement agency, the Coast Guard is not subject to the Posse Comitatus Act.

As part of his plan to secure America’s borders, former President Trump (along with his challengers in the Republican presidential primary) has proposed sending U.S. military personnel to the southern border. During his administration, then-President Trump even considered declaring a state of national emergency due to the border crisis. 

While some claimed that Trump lacked the legal authority to declared a state of national emergency, others claimed that sending troops to the border violates Posse Comitatus. For example, Representative Ted Lieu (D-CA) declared it would be “illegal” for President Trump to declare a national emergency and send troops to the southern border, stating “it would violate the Posse Comitatus Act.” Congressman Lieu, who claims to have “studied this issue” as a military attorney, is incorrect, and to understand why, it’s important to understand how both issues are connected.

The president clearly has the authority to declare a state of national emergency. Less clear is whether a declared state of emergency qualifies as one of the “circumstances expressly authorized by the Constitution or Act of Congress” in which Posse Comitatus allows the deployment of troops. Resolving that question through months, or years, of litigation is probably less-than-desirable for a president seeking to address a crisis. Fortunately, Congress has already taken specific actions that obviate the need for litigation.  

Under the Fiscal Year 2007 National Defense Authorization Act, Congress granted the president the authority to mobilize the military to “restore public order and enforce the laws of the United States” under a number of circumstances, to include “a condition that opposes or obstructs the execution of the laws of the United States.” Congress also authorized the Secretary of Defense to, upon request from the Secretary of Homeland Security, assist in domestic law enforcement efforts to prevent terrorists, illegal drugs, and illegal aliens from entering the United States.

In other words, the Posse Comitatus Act’s own exception can be triggered under the conditions outlined in the 2007 NDAA. Thus, it is not an absolute prohibition on the domestic use of military forces. Indeed, in 2005, Congress issued a Joint Resolution stating that:

[B]y its express terms, the Posse Comitatus Act is not a complete barrier to the use of the Armed Forces for a range of domestic purposes, including law enforcement functions, when the use of the Armed Forces is authorized by Act of Congress or the President determines that the use of the Armed Forces is required to fulfill the President's obligations under the Constitution to respond promptly in time of war, insurrection, or other serious emergency.

Were a president to actually send troops to the southern border, it would not be unprecedented. In 2006, President George W. Bush deployed roughly 6,000 troops to the border to support domestic law enforcement activities. In 2010, President Obama took similar action. And notably, President Biden has also sent troops to the border. Although those actions might have been unpopular in some quarters, no one seriously questions whether Presidents Bush, Obama, and Biden violated the Posse Comitatus Act.

Whether a president should deploy federal troops to the southern border is a question best left to policy experts. But there can be no question that a president certainly can deploy those troops, should he decide to do so.

Note from the Editor: The Federalist Society takes no positions on particular legal and public policy matters. Any expressions of opinion are those of the author. We welcome responses to the views presented here. To join the debate, please email us at info@fedsoc.org.