Leonard Schlup, "Williams, George Henry," American National Biography Online, February 2000, http://www.anb.org/articles/05/05-00959.html.
Becoming increasingly dissatisfied with the Democratic party during the course of the Civil War and pleased with the policies of President Abraham Lincoln, Williams joined the Republican party in 1864. That year the Oregon state legislature elected him as a Republican to the U.S. Senate, where he served from 1865 to 1871.... Williams supported the Radical Republicans, including Representative Thaddeus Stevens of Pennsylvania, in attempts to impose a strict policy of Reconstruction on the vanquished South. He wrote the Reconstruction Act of 1867, which reorganized the Confederate states under military governors. His position on Reconstruction was further refined in a Senate speech on 4 February 1868. A member of the Joint Committee on Reconstruction and of the Senate Committee on the Judiciary, he opposed President Andrew Johnson. Williams introduced the Tenure of Office Act of 1867 to prohibit the chief executive from removing cabinet members and other civil officials without senatorial approval, fearing that the southern president might replace loyal Republicans appointed by Lincoln with former rebels. Congress passed this controversial measure over Johnson's veto. In 1868 Williams was one of the chief advocates of the impeachment of Johnson.