参议院席位空缺的原因多种多样——参议员在任期内去世、不光彩辞职或辞职担任另一职位，通常是当选或任命的政府职位。

当参议员在任期内去世或辞职时会发生什么？如何处理替换？

《美国宪法》第一条第3节概述了参议员的选举程序，后来经第十七（17）条修正案第2款修正。1913年批准的第17条修正案不仅改变了参议员的选举方式（普选直选），还概述了如何填补参议院空缺：

When vacancies happen in the representation of any State in the Senate, the executive authority of such State shall issue writs of election to fill such vacancies: Provided, That the legislature of any State may empower the executive thereof to make temporary appointments until the people fill the vacancies by election as the legislature may direct.

这在实践中意味着什么？

美国宪法授予州立法机构决定如何替换美国参议员的权力，包括授权首席执行官（州长）做出这些任命。

一些州要求举行特别选举以填补空缺。有几个州要求州长任命一名与前任执政者相同的政党的替代者。通常情况下，继任者将任职到下一次预定的全州选举。

国会研究局：

Prevailing practice is for state governors to fill Senate vacancies by appointment, with the appointee serving until a special election has been held, at which time the appointment expires immediately. In the event a seat becomes vacant between the time of a general election and the expiration of the term, however, the appointee usually serves the balance of the term, until the next regularly scheduled general election. This practice originated with the constitutional provision that applied prior to the popular election of senators, under which governors were directed to make temporary appointments when state legislatures were in recess. It was intended to ensure continuity in a state’s Senate representation during the lengthy intervals between state legislative sessions.

例外情况或州长没有无限权力的情况

阿拉斯加、俄勒冈州和威斯康星州不允许州长做出临时任命；州法律要求进行特别选举以填补参议院的空缺。

俄克拉荷马州还要求参议院空缺由特别选举填补，但有一个例外。如果空缺发生在偶数年的3月1日之后，任期在下一年届满，则不举行特别选举；相反，总督必须任命在常规大选中当选的候选人，以填补未满的任期。

亚利桑那州和夏威夷州要求州长任命一名与前任州长隶属同一政党的人士填补参议院空缺。

犹他州和怀俄明州要求州长从前现任州长所属政党的州中央委员会提出的三名候选人名单中选出一名临时参议员。

如果参议员死亡，其工作人员将继续获得不超过60天的补偿（除非参议院规则和行政委员会确定需要更多时间来完成办公室关闭），在参议院秘书的指导下履行职责。