At least two of those races are tight. The Illinois race between Democrat Alexi Giannoulias and Republican Mark Kirk is a dead heat, while Republican John Raese is gaining ground on Democrat Joe Manchin in West Virginia. That raises the realistic possibility that the Democrats' 59-seat majority in the Senate could shrink by one, if not two, during the lame-duck session.
Ahead of the election, both sides are seizing on the stalemate in Congress as evidence that the opposing party has failed.
Democrats highlight that the current Congress has passed major pieces of legislation including health care reform, the economic stimulus package and the Wall Street regulatory overhaul -- all in the face of steadfast GOP opposition.
"This has been one of the most productive sessions of Congress despite efforts by Republicans to obstruct and delay nearly everything we have tried to do," said Regan Lachapelle, spokeswoman for Senate Majority Leader Harry Reid. "We are continuing our efforts to create jobs and strengthen the economy, and we will consider appropriations legislation before the end of the year."
In response, Republicans argue that Democrats are due for a loss at the polls this fall.
"Funding the government is one of the most basic responsibilities of any Congress, and the Democrat super-majority hasn't passed a single appropriations bill," a GOP aide told ABC News. "In the real world, anyone would be fired from their job for neglecting their responsibilities like that. Oh wait, Democrats will meet the real world on Nov. 2."