On April 19 and 27, 1861, Lincoln issued proclamations authorizing a blockade of Confederate ports. Congress did not recognize a state of war until July 13. During that interval of almost three months, the Union Navy captured a number of merchant vessels, and those seizures were challenged in court on the basis that Lincoln had exceeded his constitutional authority.

When the prize cases reached the Supreme Court in 1863, the justices ruled by a five to four majority that the president had acted constitutionally. While only Congress could declare war, the chief executive did have a lawful responsibility to take measures to resist insurrection. The court thus sanctioned Lincoln's exercise of emergency powers prior to the congressional authorization of those powers.