Complex sentence: In 1875, he pragmatically turned down the Democratic Nomination for Lieutenant Governor of Iowa, since from the office establishment in 1858 and until 1892, only Republicans occupied the office.
Split into simpler sentences: In 1875, he pragmatically turned down the Democratic Nomination for Lieutenant Governor of Iowa. At the time, from the office establishment in 1858 and until 1892, only Republicans occupied the office.