The Confederates did exactly that, sending three commissioners to D.C. to discuss the matter with the Lincoln administration. They were assured by the U.S. Secretary of State, William Seward, that Ft. Sumter would be evacuated, and that the administration had no plans to resupply it. The Confederates assumed that the Sec. of State spoke for Lincoln, but that was obviously not the case.
they were in a hurry to fight this war....they were winning this war...but ultimately lost it...
this fort and other USA forts in CSA territories might have taken months...no years to pass into CSA hands...
I have no ax to grind...I live up North(hopefully not for the rest of life)but my forebears were stomping grapes in some bucolic little southern european village or harvesting potatoes in some equally bucolic northern european village....I am a states rights constitutional type...but I do believe the South made some fundamental political and military blunders and the attack on Sumter was the first and probably the worst....