The president has the authority to use military forces to defend our country's territory. The president also has authority, by law and by precedence, to use military forces to support civil authorities in preserving the peace.

I note this in light of Tara Copp's report for the Military Times on Wednesday, which explains that the White House has authorized U.S. military personnel stationed at the U.S.-Mexican border to use force in support of Border Patrol and law enforcement authorities. This use of force entails actions that the "Secretary of Defense determines are reasonably necessary," including "a show or use of force (including lethal force, where necessary), crowd control, temporary detention, and cursory search."

That authorization has some commentators enraged. They claim President Trump is about to shred federal law relating to the Posse Comitatus Act, which prevents the military's use in most civilian law enforcement matters.

They are wrong. While I don't believe the military's border mission is necessary, Trump has the legal authority to determine that its deployment is necessary. For a start, there should be very little legal controversy in the military's employment to defend the border against an unlawful incursion by foreign nationals. The defense of territory and persons, after all, is the primary responsibility of the Department of Defense. But while there are noted precedent exclusions to Posse Comitatus that allow the military to support civilian authorities in matters relating to national disasters and counterterrorism etc., there are other authorities also relevant here — specifically, the provisions under federal law as vested under Title 10, Chapter 13 of the U.S. code.

That chapter includes an authority grant that:



Whenever the President considers that unlawful obstructions, combinations, or assemblages, or rebellion against the authority of the United States, make it impracticable to enforce the laws of the United States in any State by the ordinary course of judicial proceedings, he may call into Federal service such of the militia of any State, and use such of the armed forces, as he considers necessary to enforce those laws or to suppress the rebellion.



I would suggest that the assemblage of migrants at the border, including dozens of suspected criminals, gives Trump cause to invoke this authority in the current border situation. But Chapter 13 also includes another authority. It notes that:



The President, by using the militia or the armed forces, or both, or by any other means, shall take such measures as he considers necessary to suppress, in a State, any insurrection, domestic violence, unlawful combination, or conspiracy, if it — (1) so hinders the execution of the laws of that State, and of the United States within the State, that any part or class of its people is deprived of a right, privilege, immunity, or protection named in the Constitution and secured by law, and the constituted authorities of that State are unable, fail, or refuse to protect that right, privilege, or immunity, or to give that protection ...



Note the wide latitude given to the president to use "such measures as he considers necessary." While the relevant qualification for military engagement is that a state authority be "unable" to protect the peace and persons of a state, thousands of migrants congregating in a focused area gives Trump grounds to believe that border states are unable to meet this challenge.

Put simply, the Trump administration has the legal authority both to order troops to the border and to afford them with the authority to use force in the service of their duties.

Yet the broader point here is that there's nothing particularly unusual about this use of military power in a democracy. In Britain and France, for example, the army is regularly called upon to support civil authorities in counterterrorism and natural disaster efforts. This includes the deployment of thousands of soldiers onto the streets. Does that shred British or French democracy? Of course not.

For all these reasons, I am highly confident that if the Supreme Court were ever to hear an appeal on this case, its judgment would be decisive in Trump's favor.