U.S. Senate election history:
1862 - 1932: since Abraham Lincoln and the inception of the republican party, until the great depression, Republicans had control of the Senate %85 of the time.
1933 - 1994: Since the great depression in 1933, Democrats had control of the Senate %75 of the time.
1995 - present: Since the first midterm of Bill Clinton, control of the U.S. Senate was almost evenly divided between both parties.