Garfield entered the Thirty-eighth Congress a strong pro-Unionist and an even stronger abolitionist. The young radical Republican began his congressional career just as the finishing touches were being completed on the Capitol dome. Garfield did not believe that the nation could endure under the black veil of slavery. Garfield advocated the abolition of slavery, confiscation of property of the slave owners of the South, and most radical of all the execution or banishment of all rebel leaders. With his booming voice and eloquent radical speeches Garfield quickly established himself as an up and coming leader of Congress.

With his radical views Garfield found Abraham Lincoln's more conservative approach to the war and the South disconcerting. When the time came for the re-nomination of Lincoln Garfield was less than enthused. The radicals in Congress tried to go over Lincoln's head by passing the Wade-Davis Bill, which would put the power of Reconstruction squarely in the hands of Congress and not in the presidents. The wise Lincoln simply defeated the bill with a pocket veto. Shortly thereafter a manifesto appeared in the New York Tribune denouncing Lincoln and warning him that Congress was to be respected and that he must support their wishes. Garfield was accused of writing this manifesto which he openly denied. When time came for his reelection Garfield faced problems at home due to his support for the manifesto. Garfield stood up at the convention in Ohio and defiantly defended his position before angrily leaving the convention. As he left the convention the stunned crowd stood and unanimously voted Garfield in for another term.