Kirk was appointed to fill Ted Kennedy's seat after the (Democratic dominated) Massachusetts legislature rushed through a special bill to give the (Democratic) governor power to make an appointment following Kennedy's death. Now, some Democrats are hinting that it might take a long time to count the votes and certify the election if Brown seems to be the winner, thus allowing Kirk to continue to serve. Republicans say that by Senate rules, Kirk is no longer a Senator after tomorrow's election. Here's some history:
The Senate subcommittee and committee concluded, based on its hearing and review, that “the term of service of a Senator appointed to fill a vacancy in an unexpired term ends on the day when his successor is elected by the people.” 1939 Congressional Record, p. 998. There was evidently no controversy among either the subcommittee or full committee regarding this legal conclusion, and the committee then presented a resolution to the Senate for adoption, expressing the view that Berry’s term of service expired on November 8, 1938, the date of the special election. As Senator Connally, a member of the subcommittee, explained to the Senate, the fact that the Tennessee statute purported to extend Berry’s term until the qualification of his successor was of no force because the statute was “plainly in conflict with the provisions of the seventeenth amendment.” Accordingly, the Senate adopted the proposed resolution without dissent. 1939 Congressional Record, p. 1058.Based on this authority, it would appear that a valid point of order could be raised as to Senator Kirk’s participation in Senate proceedings after January 19, 2010.
Of course, the Senate is the judge of its own rules so it's not beyond the Democrats to change the rules. It seems strangely appropriate that Kirk could push Obamacare through as a lame duck with questionable legitimacy in a naked power grab by the Democrats.