Complex sentence: He served as United States Secretary of Labor from 1921 to 1930 under Presidents Warren G. Harding, Calvin Coolidge, and Herbert Hoover, and resigned upon his election to the United States Senate from Pennsylvania, where he served until 1945.
Split into simpler sentences: He served as United States Secretary of Labor from 1921 to 1930 under Presidents Warren G. Harding, Calvin Coolidge, and Herbert Hoover. He resigned as Secretary of Labor upon his election to the United States Senate from Pennsylvania, where he served until 1945.