Complex sentence: Weicker only served one term in the House before being elected to the U.S. Senate in 1970; he served in the U.S. Senate for three terms, from 1971 to 1989, before being defeated for a fourth term by Joe Lieberman.
Split into simpler sentences: Weicker only served one term in the House before being elected to the U.S. Senate in 1970. He served in the U.S. Senate for three terms, from 1971 to 1989, before being defeated for a fourth term by Joe Lieberman.