in Western Montana. Through the paper's editorial stance, Mantle became a Republican leader and largely shaped the party's organization and policies in Montana. He was elected to the legislature of Montana Territory in 1882. When John Schuyler Crosby left the territorial governorship in 1884, Mantle was the candidate of Western Montana to replace him, but Eastern Montana Republicans prevailed in obtaining the appointment for B. Platt Carpenter. Mantle was a delegate to the 1884 Republican National Convention, and supported George F. Edmunds for president. In 1886, Mantle was elected to a second term in the Territorial House. When the Northern Pacific Railway attempted to obtain large grants of land in Montana from the federal government, Mantle was chosen president of the Mineral Land Association, the citizens' group formed to oppose the Northern Pacific. The association's lobbying and legal efforts proved successful, and the NP did not acquire the land it sought. In 1888, Mantle was again elected to the legislature, the territory's last, and he was chosen to serve as Speaker of the House. When Montana was admitted to the Union in 1890, Mantle was a candidate for the U.S. Senate, and narrowly lost in the legislature's Republican caucus to Wilbur F. Sanders and Thomas C. Power, who were elected. In 1890 and 1892, Mantle was chairman of Montana's state Republican convention. In 1892 he was elected chairman of the state Republican executive committee. He was also elected mayor of Butte in 1892, and he served one term. When Sanders' U.S. Senate term expired in 1893, the Montana Legislature was unable to agree on a successor. Governor John E. Rickards appointed Mantle to fill the vacancy, but the Senate refused to seat him on the grounds that the governor could not make an appointment while the legislature was in session. Also in 1893, Mantle was named chairman of the state commission that organized Montana's participation at the World's Columbian Exposition in Chicago. United States Senator Sanders' seat remained vacant until January 1895, when the legislature elected Mantle as his successor. He served one partial term, January 16, 1895 to March 3, 1899. In the Senate, Mantle served on the Finance Committee, where he worked to obtain passage of amendments to the Dingley Act tariff which were favored by the National Wool Growers Association. Mantle was also an advocate of the Free silver movement, which many Montana miners favored in the