During the American Civil War, Deuster was widely reviled as a prominent Copperhead, as he opposed the abolitionist influence on the Lincoln administration and defended General George B. McClellan against his critics.

He encouraged negrophobia in his immigrant readers, warning that emancipation and abolitionism would lead to a "Negrocracy" as free whites were forced to compete with cheaper "black cattle," and referred to the abolitionist Milwaukee Herold as part of the "German Nigger Press".

Abraham Lincoln, described in the See-Bote as "the most incapable of statesmen and the most irresponsible of the butchers of men", was defended only when Deuster saw him as being harried by the more radical elements within the Republican Party.

Unlike some Copperhead newspaper editors, Deuster publicly mourned Lincoln's assassination, expressing a fear that it would give free rein to the Radical Republicans and unleash a policy of "retribution and revenge".

He was elected to the Wisconsin State Senate's Sixth District (the 3rd, 4th, 5th and 8th Wards of the City of Milwaukee, and the Towns of Franklin, Greenfield, Lake, Oak Creek and Wauwatosa) in 1870, with 2178 votes to 1704 for incumbent Charles H. Larkin, a one-time War Democrat who chose to run as an independent.

Deuster was narrowly elected in 1878 as a Democrat to the Forty-sixth Congress to succeed retiring Democratic incumbent William Pitt Lynde in Wisconsin's 4th congressional district (Milwaukee, Ozaukee and Washington counties) with 11,157 votes to 11,022 for Republican former Assemblyman Leander Frisby and 1,351 for Greenbacker and former National Union Assemblyman Truman H. Judd[4] He served as chairman of the Committee on Expenditures on Public Buildings.

There is no source to prove that he and Joseph were related to John H. Deuster, although they were all three born in Prussia, moved to Milwaukee, and became active Democratic Party politicians and legislators.