When can the U.S. President deploy military on U.S. soil?

The Hindu

5 hours ago

The story so far: Widespread protests have erupted in Los Angeles, California, after raids by U.S. Immigration and Customs Enforcement (ICE) led to dozens of arrests. In response, U.S. President Donald Trump has deployed about 4,000 national guard troops and 700 marines.
Can military be deployed in U.S.?
Military troops, including national guard units, are barred from civilian law enforcement under the Posse Comitatus Act (1878), unless explicitly authorised by the Constitution or an Act of Congress. Such authorisation is provided through the Insurrection Act which permits the President to deploy the military during civil unrest. This can be done at a State's request, or unilaterally to enforce federal law, suppress rebellion, or protect civil rights when a State government is unwilling or unable to act.
Notably, unlike other U.S. military branches, the national guard can be deployed by both the States and the federal government. They respond to domestic emergencies, overseas combat missions, counter-drug efforts, and more. Each of the 50 U.S. States maintains its own unit, which typically reports to its respective State Governors and is thus exempt from the Posse Comitatus Act. However, when 'federalised' (called into federal service), these Guards temporarily become part of the 'federal armed forces' and are subject to the said Act until returned to State control.
How has it been used in the past?
U.S. Presidents have long deployed the national guard for civil unrest, but federalising it to support law enforcement directly against protests began only in 1967. The guard's federalised role expanded in the Civil Rights era, during protests for school desegregation, and the 1965 Selma-Montgomery March. Subsequently, President Lyndon B. Johnson deployed them for the 1967 Detroit Rebellion and after Martin Luther King Jr.'s assassination in 1968. Richard Nixon and George H.W. Bush have also deployed them during various instances.
Is the Governor's consent necessary?
Mr. Trump's memorandum, instead of invoking the Insurrection Act, likely due to its widely recognised abuse potential, cites Section 12406 of Title 10 of the U.S. Code. This provision allows the President to call national guard members into 'federal service', under certain circumstances, including rebellion against federal authority. Traditionally, Presidents have used Section 12406 as the procedural mechanism along with the Insurrection Act's substantive powers, invoking both to justify deployment.
Interestingly, Mr. Trump has attempted to decouple these authorities. In federalising and deploying the national guard, he appears to rely either on Section 12406 as a standalone power or pair it with claimed 'inherent' constitutional authority (Article II of the Constitution), citing his Presidential duty to protect federal personnel, property, and functions. For active-duty military deployment, he seems to lean solely on inherent constitutional power, as Section 12406 does not authorise using active-duty armed forces for such purposes. However, this employed legal framework lacks the 'unambiguous authority' that the Insurrection Act provides to engage troops. Under Title 10, the President's authority to deploy the national guard without the Governor's consent is ambiguous — while the first part of the provision allows federalisation, another mandates that orders 'shall be issued through the governors'.
On June 9, California Attorney General Rob Bonta and Governor Gavin Newsom sued President Trump and Defence Secretary Pete Hegseth, calling the unilateral federalisation of California's national guard an 'unlawful' overreach.
How does it work in India?
Article 355 of the Constitution mandates the Union to protect States against 'external aggression' and 'internal disturbance'. This allows the Centre to deploy the army even without a State's request. While 'public order' is a State subject, the Union can deploy armed forces to aid 'civil power' under Entry 2A of List I. In Extra-Judicial Execution Victim Families Assn. versus Union of India (2016), the Supreme Court held that armed forces deployment supplements, not supplants, a State's continuing civil power. Crucially, deployment must be withdrawn once normalcy is restored; normalcy not being restored cannot serve as a fig leaf for prolonged, indefinite, or permanent military presence.
Kartikey Singh is a lawyer based in Delhi.