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A Proposed Immigration Policy that Challenges Separation of Powers

The plan would flout constitutional and statutory limits.

This piece was originally published by Just Security.

Late last month, Florida governor and presidential candidate Ron DeSantis announced “Mission: Stop the Invasion,” his campaign’s proposal for reducing the flow of fentanyl and slowing migration across the U.S.‑Mexico border. The opioid epidemic and immigration enforcement pose some of the most challenging policy questions that leaders and lawmakers face today – so it comes as no surprise that a 2024 hopeful would announce a plan for the border. DeSantis’s proposal, however, offers no serious solutions. Instead, “Mission: Stop the Invasion” traffics in troubling rhetoric and overbroad, even unconstitutional, articulations of presidential power.

Commentators have already challenged the legality of the DeSantis proposal insofar as it promises to end birthright citizenship. We highlight a separate set of legal concerns, based on how DeSantis has proposed using the U.S. military in Latin America and at the border.

U.S. Military in Mexico

In “Mission Stop the Invasion,” DeSantis outlines various policies designed to stem the flow of drugs from Mexico. In the most concerning of these proposals, DeSantis promises to “hold cartels accountable” through “direct action as needed.” He suggests sending U.S. forces across the border if Mexico “drags its feet” on countering narcotics traffickers. In short, DeSantis threatens to use military force in Mexico, potentially without the consent of the Mexican government.

But the president lacks the legal authority to use military force against cartels in Mexico. Congress, not the president, has the constitutional authority to decide when, where, and with whom the nation is at war. The Constitution specifically gives Congress the power to declare war and to create, fund, and regulate the military. It does not enumerate any presidential war powers. And while the Constitution refers to the president as Commander in Chief, the Founders and later the Supreme Court clarified that this role means serving as “first General and admiral” of the military, after Congress has already “provide[d] by law for carrying on war.”

Congress has not provided by law for carrying on a new war in Mexico – though there is ongoing debate over whether it should. Certain members of Congress have introduced legislation that would authorize hostilities against a list of named cartels. Other lawmakers have responded by offering language that would prohibit the president from using federal funds for forcible action in Mexico. The president cannot bypass this democratic process, in essence deciding for Congress that military force is appropriate. 

Nevertheless, it is possible that DeSantis intends to rely on controversial interpretations of the president’s authority to use defensive force as a pretext for dragging the country into a new war. When the Founders gave Congress the prerogative to declare war, they were clear that this would not foreclose the president from using force to “repel sudden attacks.” For much of American history, this was understood to permit unilateral presidential action only for the purpose of thwarting imminent or ongoing assaults on U.S. persons and territory. Since the Cold War, however, executive branch lawyers have articulated an ever‑growing set of circumstances under which the president may defend not only the homeland but also abstract “vital national interests.”

The standard for identifying vital national interests is open-ended enough – indeed, respected commentators have described it as “meaningless” – that DeSantis could assert that the president’s power to use military force extends to preventing drug trafficking. Alternatively, DeSantis may be able to conjure up a rationale for pursuing Mexican cartels if Congress enacts legislation that unwittingly dovetails with one of the many interests that previous presidents have deemed sufficient to justify congressionally unauthorized hostilities. Of greatest present concern is the House’s Project Precursor Act, which, if enacted, would signal Congress’s belief that fentanyl is a chemical weapon. In 2018, executive branch lawyers issued an opinion saying that the president can use military force to “deter[] the use and proliferation of chemical weapons,” even in the absence of congressional approval. 

U.S. Military in Panama and Colombia

DeSantis’s plan for slowing migration also raises war powers concerns, this time regarding U.S. involvement in Panama and Colombia. In “Mission: Stop the Invasion,” DeSantis promises to “close” the Darién Gap, the isthmus between Panama and Colombia that South American migrants and asylum‑seekers must cross en route to the U.S.-Mexico border. Multiple armed groups and combatants in the Colombian Civil War, such as the Revolutionary Armed Forces of Colombia (FARC) and the Gaitanist Self-Defense Forces of Colombia (AGC), are known to operate in the Darién. Congress has not authorized the use of military force against any of these groups.

Although “Mission: Stop the Invasion” is short on details for how DeSantis would “shut down crossings” in the Darién, the proposal gestures toward security cooperation, i.e., work with military partners in Panama and Colombia. To some extent, “Mission: Stop the Invasion” maps onto action already undertaken by the Biden administration. According to a congressional staffer with whom we spoke, the Department of Defense has deployed personnel to provide training in support of Panama’s “Operation Shield” and Colombia’s “Operation Darién,” efforts by those countries’ national security forces to curb armed groups’ activity, particularly human smuggling, in the Darién. 

This ongoing deployment is concerning and warrants more congressional and public transparency from the Biden administration. Even when U.S. forces are deployed to train and advise partners, rather than conduct combat operations, they can end up in hostilities if they are stationed in locations where they or their partners are likely to come under attack. Given the volatility of the Darién, it is possible, and perhaps probable, that U.S. forces in the region will be targeted by armed groups – particularly if U.S. forces are co-located with Panamanian or Colombian partners who are actively combating those groups. It is also possible that U.S. forces will enter the fight to prevent their partners from taking casualties, under an overbroad and controversial theory of presidential power known as “collective self‑defense.” In countries around the world, U.S. train-and-advise missions have embroiled the United States in hostilities that Congress never authorized.  

Notwithstanding the risk of unauthorized hostilities, it seems that DeSantis wants to double down on the Biden administration’s deployment. “Mission: Stop the Invasion” proposes closing the Darién Gap, with the explicit goal of stopping migrants and asylum-seekers. This goes beyond the current scope of U.S.‑backed efforts in the Darién, which reportedly do not aspire to a total closure of the border and do not target migrants or asylum-seekers, as opposed to transnational criminal organizations involved in human smuggling.

Expanding the U.S. military footprint in the Darién would increase the risk of unauthorized hostilities. And shifting the focus of the deployment could exceed the scope of the Department of Defense’s current authorities for working with foreign partners. Under existing authorities, like the global train-and-equip authority at 10 U.S.C. § 333 or the Plan Colombia authority at § 1021 of the National Defense Authorization Act for Fiscal Year 2005, U.S. forces can train, equip, and assist foreign partners to counter terrorism, narcotics trafficking, and transnational organized crime. These authorities, or others like them, likely support the Biden administration’s current deployment. But they do not clearly support the kind of pure immigration enforcement that “Mission Stop the Invasion” seems to contemplate.

U.S. Military at the Southern Border

Two elements of DeSantis’s “Mission: Stop the Invasion” plan, when read together, would also run afoul of legal restrictions on the U.S. military’s domestic activities unless DeSantis were to invoke the Insurrection Act, a statutory authority intended for use only the most extreme emergencies.

Under the “No Excuses: Build the Wall” section of DeSantis’s plan, the first bullet point reads, in part, “DeSantis will use the military to assist the border patrol on day one.” Of course, the military is already assisting CBP at the southern border right now, under the Biden administration. Indeed, the armed forces’ involvement in border enforcement has been steadily growing for the past forty years, with little public examination and regardless of who has been in the White House or in control of Congress.

Where DeSantis breaks new ground is in the duties he apparently intends to assign to these troops. In the section titled “No Excuses: Hold Cartels Accountable,” the fourth bullet point reads, “DeSantis will authorize appropriate rules of engagement at the border so that those trying to smuggle drugs into the United States are met with the use of force.” Although he does not specify as much, this broad, undifferentiated statement presumably applies to the rules of engagement for both CBP agents and the U.S. military personnel.

If so, that would be a dramatic break from current practice and would raise multiple legal questions. Most of what the military does at the border today – manning static observation posts, clearing vegetation, maintaining CBP vehicles, and maintaining and operating surveillance equipment, among other things – is plainly authorized by two statutes: 10 U.S.C. §§ 274 and 284. However, nothing in the text of these provisions appears to allow U.S. military personnel to perform duties that involve the use of force. Indeed, another statute, 10 U.S.C. § 275, indicates that Sections 274 and 284 do not permit “direct participation by a member of the Army, Navy, Air Force, or Marine Corps in a search, seizure, arrest, or other similar activity unless participation in such activity by such member is otherwise authorized by law.”

Using the military to forcibly confront drug smugglers would thus violate the Posse Comitatus Act. This law bars federal military forces from participating in civilian law enforcement activities unless doing so has been expressly authorized by Congress. While there are a number of statutory exceptions to the Act – including, most notably, the Insurrection Act – it remains the most important restriction on the U.S. military’s domestic activities. The Posse Comitatus Act and the Insurrection Act also reflect a core constitutional principle, established by the Calling Forth Clause and recognized by the Supreme Court, that Congress, not the president, controls what the military can and cannot do inside the United States. 

The federal courts have said that military assistance to law enforcement implicates the Posse Comitatus Act if the military’s activities (1) “constitute the exercise of regulatory, proscriptive, or compulsory military power,” (2) “amount to direct active involvement in the execution of the laws,” or (3) “pervade the activities of civilian authorities.” An activity runs afoul of the Posse Comitatus Act if it meets any one of these tests, and DeSantis’s plan would meet all three. First, the use of force by military personnel would amount to the most literal possible exercise of “compulsory” military power. Second, searches and seizures are core law enforcement functions, and the Supreme Court considers a “seizure” to have occurred whenever a government official shoots a person or otherwise applies physical force to the body with intent to restrain. And third, the activities of CBP would undoubtedly be pervaded by military involvement if CBP agents and federal military personnel were using force side-by-side against alleged smugglers. 

While there are numerous statutory exceptions to the Posse Comitatus Act, the only one that could conceivably apply here is the Insurrection Act. This law allows the president to deploy the military domestically and use it to suppress insurrections or enforce the law under certain circumstances. It is designed for transient emergencies that leave civilian authorities surprised and overwhelmed, not long-standing policy challenges like drug smuggling across the U.S.-Mexico border. In the modern era, it is also rarely used. If DeSantis were to invoke the Insurrection Act to deploy the armed forces against alleged smugglers at the border, he would be the first president to use the law in more than thirty years

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As the field for the 2024 presidential election shapes up, “Mission: Stop the Invasion” is one of the first in a likely array of proposals for addressing the opioid epidemic and immigration enforcement. But it must not set the standard. DeSantis has proposed action both abroad and at home that would flout constitutional and statutory limits. DeSantis should reconsider this approach, and all candidates should ensure that their policies for securing the U.S.-Mexico border respect the separation of powers.