all of the following contribute to the success of incumbent members of congress in election campaigns except: (a) incumbents usually raise more campaign funds than do their challengers. (b) incumbents tend to understand national issues better than do their challengers. (c) incumbents are usually better known to voters than are their challengers. (d) incumbents can use staff to perform services for constituents. (e) incumbents often sit on committees that permit them to serve district interests.