“The federal government had 2 distinct functions. To deal with incoming goods and governments of foreign countries, and to act as a city government for the city-State known as the District of Columbia.”
That’s not true, and I think you know it. How is it possible you’re not aware it had the power to govern relations between the states, as well?
Only if you mean the ability to arbitrate between the entities of the States and NOT the physical States themselves.
If that's the case, you are correct and the error was mine. I should have said 3.