Reasons why incumbent senators have greater competition than incumbent members of the House include all of the following reasons
a. an entire state is more diverse than a Congressional district, providing more of a base for opposition.
b. voters are less likely to know the issue positions of their senators than their representatives.
c. Senators have less personal contact with their constituencies.
d. Senate challengers are better funded than House challengers.
e. Senators tend to draw more visible challengers.