Executing a Slave Trader:
Early in the war, Lincoln approached the issue of slavery with caution. He focused on his stated purpose, to maintain the Union, and on not losing the support of the "border" states in which slavery was legal. He did, however, become the only president to approve the execution of a slave trader.
(Document) Abraham Lincoln's respite of execution for the slaver Nathaniel Gordon, countersigned by Secretary of State William H. Seward, February 2, 1862. In this document, Lincoln refuses to commute the sentence of Nathaniel Gordon, convinced of engaging in the international slave trade (which the Constitution prohibited after 1808), but grants him a brief period of leave to prepare for his execution on February 21, 1862.