It is possible for a felon to serve in the U.S. Congress – but the House and Senate can vote to expel any member that colleagues deem unfit or unqualified to serve.  And even if Stevens does end up winning the election in Alaska, he faces a probable expulsion vote in the Senate. He says he’ll appeal his conviction, and he has yet to be sentenced.

Update: Begich was declared the winner of the election on Nov. 18.

Federal office qualifications are governed by the Constitution, while state-level office rules vary according to state laws.

The Constitution requires that members of the House and Senate fulfill three requirements:

• All members of the House must be at least 25 years old, and members of the Senate must be at least 30 years old.
• Members of the House must have been a U.S. citizen for at least seven years, and members of the Senate must have been a U.S. citizen for at least nine years.
• They have to be an "inhabitant" of the state "when elected."

CRS: [S]ince a State does not have the authority to add qualifications for federal offices, the fact of conviction, even for a felony offense, could not be used to keep a candidate off of the ballot under State law either as a direct disqualification of convicted felons from holding or being a candidate for office, or as a disqualification of one who is no longer a “qualified elector” in the State. Once a person meets the three constitutional qualifications of age, citizenship and inhabitancy in the State when elected, that person, if duly elected, is constitutionally “qualified” to serve in Congress, even if a convicted felon.

Prison is not a bar to running for federal office, either. In 1798, Rep. Matthew Lyon ran for Congress from prison and won. He assumed his seat in Congress after serving four months in prison for "libeling" President John Adams. An effort was made to expel Lyon from the House, but it failed.

Ultimately, it is up to the House or Senate chamber to determine whether or not an elected official is qualified to serve if a challenge is raised.