Article I, Section 3 of the US Constitution sets three qualifications for senators: 1) they must be at least 30 years old, 2) they must have been citizens of the United States for the past 9 years or longer, and 3) they must be inhabitants of the states they seek to represent at the time of their election. The age and citizenship qualifications for senators are more stringent than those for representatives. In Federalist No. 62, James Madison justified this arrangement by arguing that the "senatorial trust" called for a "greater extent of information and stability of character".

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