Railroads were shameless thieves in the robber baron period.
It is probably accurate to say that most of the robber barons were Republicans.
But in the late 1800's and early 1900's, the reformers were former Republicans before they started advocating reforms, like Bob LaFollette and his Progressive Party.
T. Roosevelt split from the GOP in 1912 to run on his own Bullmoose Party platform. He lost, and Wilson won.
I can't say that I think the country would have been better off had TR won. The US getting into WWI was a terrible idea, and TR liked wars.