Now that is just utter nonsense. Trying to land supplies to your troops in your fort is not an act of aggression. Trying to starve them into submission and then bombarding them into surrender is.
If the United States stood an invasion fleet into Tampico Bay, I rather imagine the Mexican Government and the local commandant would do the same thing Beauregard did.
Now that's a silly analogy. The U.S. does not have a fort in Tampico.
The United States no longer had the right to maintain troops there, to occupy or garrison the fort, or to stand up a task force, which is what Lincoln sent (don't say "resupply" -- that's just an old Lincolnian lie: there were a lot of troops in that flotilla).
Sumter was no longer United States property, South Carolina having demanded its return. The United States no longer had title to any property on the territory of South Carolina, which had reclaimed her sovereignty under international law, as an exercise of the natural and sovereign rights of her People.