Qualifications for Senators
No Person shall be a Senator who shall not have attained to the Age of thirty Years, and been nine Years a Citizen of the United States, and who shall not, when elected, be an Inhabitant of that State for which he shall be chosen.
The Framers understood that the frequent elections for Members of the House meant that Congress as a whole could be subject to the dangers of faction unless a “responsible” Senate were added to the legislature. Publius argued in The Federalist No. 63 that the role of the Senate ensures that “the cool and deliberate sense of the community” prevails in Congress over the potential tyranny of momentary passions. In The Federalist No. 62, he explained that the more advanced age of Senators and their longer period of citizenship would make them better suited for the “senatorial trust, which, requiring greater extent of information and stability of character, requires at the same time that the senator should have reached a period of life most likely to supply these advantages.” Before the Constitutional Convention settled on a required nine-year citizenship compromise, Gouverneur Morris had pressed for a fourteen-year period of citizenship. It would take at least that long, Morris argued, for foreigners to learn the American Constitution and its system of laws. James Madison, Benjamin Franklin, and James Wilson opposed a period of such length, arguing that it would make the Constitution too “illiberal.”
The age, residency, and citizenship requirements for the Senate have not, themselves, been the subject of judicial dispute. The clause makes it clear that one must be a resident of the state at the time of election, but the Senate has adopted the practice of receiving into its membership Senators who attain the minimum age or length of citizenship subsequent to their election but prior to assuming office.
In the aftermath of the Civil War, both Houses of Congress did occasionally deny individuals their seats if they could not swear that they had never been disloyal to the union. The question of Congress’s power to consider qualifications in addition to those stated in Article I remained open until 1969, when Chief Justice Earl Warren wrote in Powell v. McCormack that “in judging the qualifications of its members Congress is limited to the standing qualifications prescribed in the Constitution.”
The question whether states could add to the Constitution’s list of requirements was the focus of United States Term Limits v. Thornton (1995). Previously, both the House and the Senate had seated Members who were not in compliance with an additional state requirement. For example, in 1856 the Senate seated Lyman Trumbull from Illinois, even though, as a sitting state judge, Trumbull was forbidden by the Illinois Constitution from serving in any other state or federal office. A 1970 circuit opinion by Justice Hugo L. Black in Davis v. Adams upheld a lower court’s determination that the state of Florida could not require a candidate for Congress to resign his state office prior to assuming his federal candidacy. In writing for the Court in Thornton, Justice John Paul Stevens concluded that “the Framers intended the Constitution to be the exclusive source of qualifications for members of Congress, and that the Framers thereby ‘divested’ States of any power to add qualifications.”
John C. Eastman, Open to Merit of Every Description? An Historical Assessment of the Constitution's Qualifications Clauses, 73 Denv. U. L. Rev. 89 (1995)
Powell v. McCormack, 395 U.S. 486 (1969)
Davis v. Adams, 400 U.S. 1203 (1970)
United States Term Limits v. Thornton, 514 U.S. 779 (1995)