Foss was politically a Republican for many years, but was an outspoken advocate of reciprocity (the lowering of tariffs with neighboring Canada), which many Republicans opposed. This position had popular support, because the tariffs were in part responsible for the high price of coal, on which the state was dependent for heat. He won nomination to a "safe seat" in 1902, and attempted to upset the party establishment from its strong pro-tariff position. This effort was squelched by party leaders (Senator Henry Cabot Lodge and Governor Winthrop Murray Crane), and Foss lost the election. He ran again in 1904, with an even more embarrassing defeat. He next failed in a bid for the Republican nomination for lieutenant governor in 1906.