Complex sentence: Nine of the states where progressive elements were strongest had set up preference primaries, which Roosevelt won, but Taft had worked far harder than Roosevelt to control the Republican Party's organizational operations and the mechanism for choosing its presidential nominee, the 1912 Republican National Convention.
Split into simpler sentences: Nine of the states where progressive elements were strongest had set up preference primaries, which Roosevelt won. But Taft had worked far harder than Roosevelt to control the Republican Party's organizational operations and the mechanism for choosing its presidential nominee, the 1912 Republican National Convention.