Quick Dig: State Secession and Military Intervention.
A quick review of the legality of using military forces in response to secession.
Regarding state secession leading to military intervention; If a state did secede from the US, all of the people there who are already US citizens would still retain their US citizenship. You don't relinquish citizenship just because you do not live in the US. So, it's not as easy to just deploy the military as the President/Congress normally could.
As I understand it, the President would have to invoke the Insurrection Act, and follow all the procedures therein, to use the military on US citizens or for law enforcement within US territory. And yes, a seceded state would likely be treated as US territory by the Federal government.
Even if a state fully seceded via democratic process, the Federal government would likely not recognize the sovereignty of that state, and thus they would still consider it US Territory; which the Federal government has a sovereign right to defend and maintain governmental functions in, by military force if necessary. So, as far as the Federal government is concerned, the Insurrection Act would most likely still be considered applicable, because even if the state is question does not consider itself US territory, the Federal government still would.
The other option would be for local military leadership to take it upon themselves to intervene on the grounds of assisting overwhelmed local law enforcement to regain control and prevent damage/destruction of federal property/assets; which is permitted under DoD policy despite being ostensibly prohibited by the Posse Comitatus Act, citing 32 CFR 215.4 (Circa 2016), which states:
"(1) The constitutional exceptions are two in number and are based upon the inherent legal right of the U.S. Government - a sovereign national entity under the Federal Constitution - to insure the preservation of public order and the carrying out of governmental operations within its territorial limits, by force if necessary.
(i) The emergency authority. Authorities prompt and vigorous Federal action, including use of military forces, to prevent loss of life or wanton destruction of property and to restore governmental functioning and public order when sudden and unexpected civil disturbances, disasters, or calamities seriously endanger life and property and disrupt normal governmental functions to such an extent that duly constituted local authorities are unable to control the situations.
(ii) Protection of Federal property and functions. Authorizes Federal action, including the use of military forces, to protect Federal property and Federal governmental functions when the need for protection exists and duly constituted local authorities are unable or decline to provide adequate protection.".
Under section 1, part i, military leaders could intervene to "... restore government functioning and public order...", if they so choose. Failing that, under section 1, part ii, military leaders could decide to intervene on the basis of needing to "... protect Federal property and Federal governmental functions...", because the local authorities have chosen to secede and thus "... decline to provide adequate protection.". In short, military leaders actually have a lot of latitude in this regard.
While it might be abnormal for the military to launch a large-scale operation without Executive or Congressional order, it’s not prohibited, and actually specifically allowed for under 32 CFR 215.4. However, it would be the sole discretion of military leadership within the seceded state to take unilateral action or not. So, how such an intervention would play out would depend on what forces are stationed within the state, and who is in command of those forces.
The final option is full-on illegal/unconstitutional, extra-judicial executive action. Which Obama already began doing with his extra-judicial drone assassination program; for which no legal action was taken to punish, thus setting a legal precedence for future allowance of such activities by other presidents since it was permitted without the initiation of adverse legal actions, despite widespread public knowledge of the crime.
Yes, the president having the military assassinate a US citizen, even in 'war' and on foreign soil, and even if they are a suspected terrorist or 'terrorist supporter', is a MAJOR crime. All US citizens have a right to fair trial by jury, and that was not afforded prior to summary execution by drone-fired missiles. Such action is completely different from invoking the Insurrection Act, as it requires additional legal procedure be conducted prior to the deployment of military force; like notifying the targeted group that force will be used if they do not disperse and cease unlawful activities, disrupting public order, governmental function, and/or destruction of property.
Given how the current administration has acted to purge military leadership of any dissent and indoctrinate troops with radical Communist/Marxist/CRT ideologies, I personally feel that the Insurrection Act will not be invoked, as that would open the administration to harsh criticism and make them responsible for the results. However, if military leadership and their troops are staunch Federal-Loyalist, indoctrinated in the ideology the seceding state is rejecting, they are likely to react unilaterally, and thus remove the need for invocation of the Insurrection Act and shield the Federal government from liability and criticism.
JB.