Complex sentence: Johnson was a Democrat from Texas who served as a United States Representative from 1937 to 1949 and as a United States Senator from 1949 to 1961, including six years as Senate Majority Leader, two as Senate Minority Leader, and two as Senate Majority Whip.
Split into simpler sentences: Johnson was a Democrat from Texas, who served as a United States Representative from 1937 to 1949 and as a United States Senator from 1949 to 1961. He spent six years as Senate Majority Leader, two as Senate Minority Leader, and two as Senate Majority Whip.