President Lincoln's papers reveal that he was preparing to use force against secessionists at least a month before Fort Sumter. On March 18, 1861, he sent a memo to Attorney General Edward Bates asking for a written opinion on a controversial matter. Speaking of himself in third-person style, he inquired whether "the Executive has power to collect duties on ship-board, off-shore, in cases where their collection in the ordinary way is, by any cause, rendered impracticable."
At the same time he posed to Secretary of the Treasury Salmon P. Chase a question to which he already knew the answer: Are there "any goods, wares and merchandise, subject by law to the payment of duties, now being imported into the United States without such duties being paid?"
With the collection of revenue listed as a major consideration for taking decisive action, on April 19 the president proclaimed a blockade of ports in seven seceded states.