How do you interpret Article I, Section 2 of the Constitution?

"The President shall be Commander-in-Chief of the Army and Navy of the United States, and of the militia of the several States, when called into the actual service of the United States;"

What does "actual service of the United States" mean? Does this mean the President is commander in chief only when war is declared?

Or is he in actual service the moment he takes the oath of office?

It seems to me that he is called into actual service from the moment he takes the oath to the time the next president takes his oath.

But if this is the case, why does it need mentioning?

They are actually talking about the National Guard (militia) when it says that. The President is not actually the Commander in Chief of the National Guard, the state's governor is, UNLESS they are called into service as a whole (such as Iraq).

And it's Article 2, section 2

It would seem to mean when we are at war based on the phrase "actual service." When you couple this with the procedure set up by the founders to place the army in "actual service," a declaration of war, it makes sense. It also reminds us of how far we have strayed from our founding principles, considering the last time we declared a war was in 1941.

It means that the militia or now as they are referred to as (State) Guard troops actually report to the Governor except when called in the actual service of the united states (such as Iraq and Afghanistan - which falls under federal )

Military can't be called to the White House to clean it up, they can to protect etc... In other words the military can't be used as a personal service of the President.