Can the Pentagon prosecute military retirees under the UCMJ? Maybe — it depends.

Scary thought but here it is. Senator Duckworth is looking to silence persons who have served this nation but don't agree with her ideology or view. Think about this, words like purge (her words) indicates a willingness to silence opposition. Like I said a scary thought.

My humble opinion - if the offense is not directly related to some form of official capacity to the respective branch, then the UCMJ does not apply. A retiree does not act in the official capacity of the military, they have no authority, and other active duty servicemembers are not subject to their orders or commands. for all intents and purposes, they are private citizens.

I would be very surprised and shocked if the military recalls any of these protestors to face UCMJ. The charges many are facing are just not significant enough to justify recalling them, and giving them all the benefits of their rank until they are found guilty. These retiree's would have to be given full pay, BAH, BAS, and other benefits determined by their needs. The cost of it far outweighs the sentence of convicting them, better to let the civilian courts deal with it.

There are some cases where military retirees can be subject to UCMJ. A recent case that the Supreme Court refused to review involved a retired Marine NCO who was drawing a pension and still in the Fleet Marine Retired Reserve. He retired at his last duty station and owned a couple of bars. He was charged with sexual assault of a bartender.
Some retirees of Active military are subject to recall and possible court martial.
Those who retired from the Reserves are generally not subject to recall and are not able to be charged under UCMJ unless it is actions related to their time in service.
I don't know how the law applies to National Guard, but I would think it would be the same as the Reserves.