Congressional districts are apportioned to the states, once every ten years, based on population figures from the most recent nationwide census.
Each of the 100 members of the Senate is elected to serve a six-year term representing the people of that person's state.
Senatorial terms are staggered, so every two years approximately one-third of the Senate is up for election.
The Seventeenth Amendment changed this to senators being elected directly by popular vote.
Controversy surrounds the question of whether the federal government or any other governmental entity has the right to regulate how many times representatives and senators can hold office.