A candidate or appointee only has three requirements to be a legitimate Senator.
Article I, Section 3 of the Constitution states: "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." (Author's emphasis) Link
Both Al Franken and Roland Burris pass muster for these requirements.
The XVII Amendment to the U.S. Constitution outlines the popular election of Senators and the authority and procedures required to replace them in case they leave for some reason.
AMENDMENT XVII
"Passed by Congress May 13, 1912. Ratified April 8, 1913.
"Note: Article I, section 3, of the Constitution was modified by the 17th amendment.
"The Senate of the United States shall be composed of two Senators from each State, elected by the people thereof, for six years; and each Senator shall have one vote. The electors in each State shall have the qualifications requisite for electors of the most numerous branch of the State legislatures.
"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.
"This amendment shall not be so construed as to affect the election or term of any Senator chosen before it becomes valid as part of the Constitution. (Author's emphasis) Link
This amendment provided for the popular election of Senators. This is so simple. Elected and appointed Senators should be immune from the actions by the any judicial, authority unless there are violations of state or federal law in the process of appointments.
But the Senate has one slim provision that can be invoked in the case of a real controversy or a contrived political event.
Article I. Section 5 states that: "Each House shall be the judge of the elections, returns and qualifications of its own members" (continues) Link
This provides the Senate with the option of rejecting a prospective member. In point of fact, there have been more than a few challenges to elections, mostly in the House. No Senator has ever been denied a seat as a result of Article I, Section 5.
(Note: You can view every article as one long page if you sign up as an Advocate Member, or higher).
