Since relief, in the form of provisioning and, perhaps, reinforcement was essential to hold Sumter, it is necessary to consider the feasibility of Fox's plan. Would Fox have been able to transport provisions or troops to the fort, either without provoking conflict or in the face of resistance? And if the plan could work, was the loss of the Powhatan, which was attached in stead to the Pickens expedition, a fatal blow to its chances?
The Fox Expedition's Feasibility
Fox himself thought his plan was "perfectly practicable," and that the Confederacy, realizing its feasibility, attacked Sumter before it could be strengthened. "I believe every officer of the army or navy present were entirely satisfied of the feasibility of . . . my plans," he declared afterwards. "In fact, their [Confederate] fire was precipitated because they . . . were assured by their best naval authority that it was perfectly practicable." Had all gone according to plan, "a reenforcement would have been easy," Fox reported after the battle of Sumter.
Fox blamed the expedition's failure on Secretary of State Seward. He claimed that Seward's "treachery" deprived him of the Powhatan, with its essential boats and crew, making the transfer of supplies and troops impossible. "Had the Powhatan arrived on the 12th," Fox wrote, "we should have had the men and provisions into Fort Sumter, as I had everything ready, boats, muffled oars, small packages of provisions, in fact everything but the 300 sailors promised to me by the [Navy] dept."
But others disagreed with Fox. Both Major Anderson and Secretary of the Navy Welles believed that Confederate forces were numerous and forewarned, making reprovisioning and reinforcement impossible. Anderson argued that the plan "could not have been successfully executed on account of the many guns which could have been brought to bear by the batteries, while Welles agreed that the effort "probably would not have succeeded" because the rebels were prepared and warned of the intended expedition.
Lincoln thought the Sumter expedition sufficiently practicable to send forward, but as he acknowledged to Fox afterwards, the "plan was not, in fact, brought to a test." In accounting for the mission's failure, Lincoln pointed to bad weather, the non-appearance of the tugboats, and his own responsibility for unintentionally depriving Fox of the Powhatan.
Bibliography: Fox, Confidential Correspondence, 1: 43-44; ORN, pp. 244-45.