If U.S. Rep. Gabrielle Giffords is incapacitated for a period of time and unable to perform her duties, there is no specific set of rules to vacate her seat.
According to the Congressional Research Service:
There is no specific protocol, procedure, or authority set out in the United States Constitution, federal law, or congressional rule for the Senate (or the House) to recognize "incapacity" of a sitting Member and thereby declare a "vacancy" in such office.
Under the general practice and operations in the Senate (as well as in the House), personal "incapacity" of a sitting Member has not generated proceedings to declare the seat vacant.
. . . it would be the particular House of Congress that would have to either declare or, at the least, recognize any such "vacancy" because of any "incapacity" before giving the oath of office and seating anyone presenting himself or herself as having been chosen to fill that seat.
In 1981, Rep. Gladys Noon Spellman of Maryland was re-elected but had a heart attack and fell into a coma before she could take the oath of office. The attending physician of Congress declared "there is no likelihood that she will be able to serve out her term of office." The House adopted a resolution declaring her seat vacant, which triggered the Maryland vacancy provision.
Arizona rules require that a special election must be called within 72 hours of the seat being declared vacant. The winner would fill the seat until 2012, when Giffords' term ends.
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