March 11-12, 1861
On March 5, after their discussion about the situation at Sumter and Pickens, Lincoln had verbally communicated the same idea to Scott when ordering the general to exercise all possible vigilance to maintain federal possessions. Lincoln apparently considered this an order to reinforce Fort Pickens. Troops were standing by aboard ships, prepared to land, and the location of the fort made it safe to reinforce from the sea. Only the arrangement worked out by Florida and the Buchanan administration stood in the way. Lincoln, therefore, was immediately carrying through on his inaugural pledge to hold federal property. The Sumter situation was, of course, more delicate due to its depleted supplies and its vulnerable location.
It is not clear that Lincoln believed he was violating a firm commitment or truce when he directed Scott to reinforce Pickens. On March 5, General Scott reported to Lincoln that the former President had established "something like a truce," or an "informal understanding," at both Pickens and Sumter. A company of reinforcements for Pickens, therefore, had not been landed at the fort, but instead remained aboard a ship lying off the fort "with orders not to land till an attack shall be made by the secessionists." A few months later, in July 1861, Lincoln stated that he knew of only "vague and uncertain rumors" about the existence of "some quasi armistace" established by the Buchanan administration. That Lincoln had only an indistinct understanding of the Buchanan truce is confirmed by Navy secretary Welles. Welles later wrote that until the afternoon of April 6, 1861, both he and the President understood only that the policy of the Buchanan administration was to "do-nothing," in return for which the secessionists would permit his administration "to expire without being molested." But neither he nor Lincoln knew of any written orders or firm agreement that committed the Lincoln administration to refrain from action.
Thus, even though Scott had informed Lincoln that President Buchanan had entered into an agreement with the secessionists regarding Sumter and Pickens, it is likely Lincoln did not consider these arrangements binding. Scott, after all, had vaguely referred to Buchanan's truce as "something like a truce," and as an "informal understanding." Further, it is evident that Lincoln considered any informal arrangements established by Buchanan as part of that administration's policy. They could not be binding on the new President.
According to Grady McWhiney, Lincoln's decision to terminate the truce at Pickens was matched by the Confederate government. Upon taking up his command in the Pensacola area, General Braxton Bragg was ordered to prepare for the "reduction of Fort Pickens." If these orders did not explicitly command the reduction of the fort, they certainly required Bragg to prepare for that eventuality.
Bibliography: McWhiney, "Confederacy's First Shot," p. 8; Lincoln, Collected Works, ed. Basler, 4: 280; Nicolay and Hay, Lincoln, 3: 393-94; Current, Lincoln and the First Shot, p. 51; Richardon, Messages and Papers of the President, 6: 22; Welles, Essays by Gideon Welles: Civil War, ed. Mordell, p. 94.