Nevada has almost always ranked near the bottom in state population, yet its leaders in Washington often have been among the nation's most powerful.

That might seem contradictory. But the key reason has been the United States Senate. Like most legislative bodies, it long has operated on the seniority system: the longer a senator serves, the likelier he or she will chair a committee, especially a powerful one like Appropriations, which doles out federal funds, or Judiciary, which considers some of the president's most important appointments.