Question

which political party of the late 1800s proposed a graduated income tax and direct election of the U.S. senators

Answer 1

The answer for your question is the Populist Party.  

The populist party of America was established in 1891 after the populist movement. The party was also known as the people’s party as it drew the strength from the farmers of south and West. Later the party was merged with the Democratic Party in 1902.  

The Populist Party was the first party who brought the 17th amendment that made Americans to elect their senators through direct voting. They also proposed a graduated income tax to make the farmers and common men America to make benefit out of it as they were the largest part of the country.