The Republican Party first came to power in the elections of 1860 when it won control of both houses of Congress and its candidate, former congressman Abraham Lincoln, was elected president. In the election of 1864, it united with War Democrats to nominate Lincoln on the National Union Party ticket; Lincoln won re-election. Under Republican congressional leadership, the Thirteenth Amendment to the United States Constitution—which banned chattel slavery in the United States—passed the Senate in 1864 and the House in 1865; it was ratified in December 1865.