Complex sentence: In 1966, he was elected to the United States Senate from Illinois as a Republican; he served for three terms (18 years) until 1985, when he was defeated by Paul Simon, and was mentioned as a GOP presidential hopeful from 1968 through 1988.
Split into simpler sentences: In 1966, he was elected to the United States Senate from Illinois as a Republican; he served for three terms (18 years) until 1985, when he was defeated by Paul Simon. He was mentioned as a GOP presidential hopeful from 1968 through 1988.