Stamped from the Beginning: The Definitive History of Racist Ideas in America by Ibram X. Kendi:
Six days after meeting with the Black delegation, Lincoln gained an opportunity to emphatically declare his views on war, emancipation, and Black people. The nation’s most powerful editor, Horace Greeley, inserted an open letter to the president in his leading New York Tribune on August 20, 1862. Greeley had been as responsible for Lincoln’s election as anyone. He urged Lincoln to enforce the “emancipation provisions” of the Second Confiscation Act.
“My paramount object in this struggle is to save the Union, and is not either to save or to destroy slavery,” Lincoln replied in Greeley’s rival paper, Washington’s National Intelligencer. “If I could save the Union without freeing any slave I would do it, and if I could save it by freeing all the slaves I would do that. What I do about slavery, and the colored race, I do because I believe it helps to save the Union.” In the New York Tribune, rising abolitionist Wendell Phillips hammered Lincoln’s remarks as “the most disgraceful document that ever came from the head of a free people.”