Director of the Richards Civil War Era Center and editor of The Journal of the Civil War Era
In this particular case, the Congress long ago had clarified the president’s power to call out the militia to put down an insurrection; however, Lincoln was in more uncharted legal territory when it came to declaring the blockade.
Lincoln had plenty of legal authority to issue his proclamation of April 15 to call out the militia to put down the rebellion. In 1792 and 1795, the Congress had passed militia acts that authorized the president to call out the militia to meet foreign threats against the nation, including states that mounted an insurrection against the government. Although not all agreed with the policy in 1861, few people argued against his power to call out the militia.
But the blockade was a different matter, primarily because of its implications for possible recognition of the Confederacy as a nation. The international community respected blockades when they featured two or more nations at war. But the Union did not want to concede that this was a war instead of a rebellion. Besides, only the U.S. Congress can declare a war, not the president. Yet, because of a quirk in the governmental calendar then, the Congress was not in session and would not resume business until December 1861. Lincoln’s imposition of the blockade on April 19 without clear guidelines from either the Constitution or the Congress, and with the possibility of legitimizing the Confederacy by suggesting that war existed, was a bold act. And it was a decision that most historians have excused.
Fortunately, the Congress gave the president a make-good. He called the legislative branch into an emergency session in July and, after the fact, the legislative branch sanctioned his actions. In fact, one of the measures that came close to a declaration of war--which never occurred--was an act passed on July 13, 1861, which empowered the president to close ports of areas deemed in insurrection against the government. The act “to provide for the Collection of Duties on Imports, and for other Purposes” can hardly be considered an inspirational call to arms for a populace, but it did allow the president to claim legal justification for his policies.