Complex sentence: Following his filibuster of Boulder Dam, Hayden did not make another speech from the floor of the Senate for twenty years and by his later years many of his congressional colleagues had not heard him make a full speech.
Split into simpler sentences: Following his filibuster of Boulder Dam, Hayden did not make another speech from the Senate floor for 20 years. By his later years, many of his congressional colleagues had not heard him make a full speech.