The US President is the Commander in Chief of the militia (when the militia is called into the actual service of the United States). And the militia, at the time of the writing of the Constitution, was every able-bodied man who was not a member of the military. Through various anti-sexism laws (though no amendment), it seems likely that this now includes able-bodied women who are not in the military.
So who all can call the militia into service and under what conditions? Can the president, for example, point at me and say, “I move you into active service. Now, as your commander, I order you to help clean Air Force One.”
Read loosely, the clause seems to allow the president the right to issue any order to any person anywhere. A tighter reading might qualify that by saying that he can only utilize the militia in the defense of the nation. A mid-range reading might expand this to defense of the nation or for the purpose of executing the laws of the nation. But I’m not sure what sort of rigmarole would be involved in moving a unit or individual in the militia into active service.
What do you think? Overall, this doesn’t seem to be a power exercised by the President so there doesn’t seem to be a lot of casework around it. But I think you could make a fairly easy case, for example, that President Obama could activate every company in the US as a militia unit and order them to spend the next 6 months prioritizing their network security over new development, to help defend the interests of the country, and he wouldn’t really need to justify the decision.