Dubois was elected as a Republican in 1890, the year Idaho became a state. He served a six-year term, and even headed the state’s delegation to the Republican National Convention in 1892 and 1896.
At that 1896 convention, there was a major split in the Republican Party. A faction of the party began calling themselves Silver Republicans. They were in favor of an expansionary monetary policy, the core of which was the minting of silver coins on demand, moving away from a gold-backed currency. It was a popular idea in Idaho and other western states where silver was plentiful. Dubois and other pro-silver Republicans left the convention in protest, forming their own party. He lost his 1896 bid for reelection.
As the turn of the century rolled around, Dubois led Idaho's Silver Republicans into a coalition with the Democrats. He became a rising star in the Democratic Party. Even so, he ran as a Silver Republican in 1900, and won. He was a Silver Republican when he was sworn in but switched to the Democratic party soon after. Dubois served one term as a Democrat, from 1901 to 1907, and did not seek reelection.