Explanation:   

   U.S. senators serve (or work in their public position) for six-year terms that are staggered, which means they don’t all begin and end at the same time.  One-third of the senators are elected every two years. With staggered terms, there are always some senators who have experience and can guide the new senators. This gives the Senate continuity. 

 

   In any organization, continuity (or the way that something stays the same over time) is extremely important. The United States Senate is no exception (or no different). If all the senators started and ended their terms (or the period of time they work in their public position) at the same time, then all the new senators would begin at the same time and nobody, or only very few people, would know how Senate meetings should be.  All of the senators would be trying to learn their new job at the same time and the Senate would not run very smoothly or easily until they did. 

 

   State legislators (or people who make laws in the government at the state level) used to elect (or choose) senators. However, since 1913, senators have been elected directly by the votes of the citizens who live in their state. Once a senator is elected, he or she can serve for the full six years before having to run for election (or try to get the public position through votes) again. Sometimes, however, senators are expelled (or forced to leave) before their term ends. This has happened only 15 times so far and the last time was in 1862. Since then, the Senate has tried to expel some senators, but those senators have resigned (or chosen to leave that job) before the other senators could make them leave. 

 

   When a vacancy (or an open position) is available, maybe because a senator has resigned or died, there is usually a special election to find a new senator to represent that state. Senators who are elected this way finish the time left in the previous senator’s six-year term and usually do not serve the full six years.

 

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