When we analyzed what we thought would happen with US House races this year, we looked at the Obama percentage in each district, the voting record of applicable House incumbents on controversial issues, and their 2008 re-election percentage. We deliberately did not perform the same analysis with the US Senate races this fall because: (1) Senate Democrats have been far more cohesive on legislation that has been voted on so far, (2) the threat of a filibuster has prevented legislation like cap and trade and “card check” from being voted on so far, and (3) only 36 senators face the voters this year (as opposed to all 435 House members).

The unexpected retirement  of Evan Bayh (D-Indiana) the day before Indiana’s Congressional filing deadline further complicates matters for the Democrats for the following reasons: (1) he never received less than 62% of the vote since his first election in 1998, so he was clearly the marquee candidate for the Democrats in that conservative state, (2) Barack Obama’s election to the Presidency, as well as subsequent cabinet appointments, created four additional races for Democrats to defend, (3) Democrats have several vulnerable and several more potentially vulnerable incumbents right now, and (4) the 6 GOP retirements are occurring at a time that an expected GOP wave can help keep those seats in the Republican column, unlike 2006 or 2008, when Democrats won nearly all of those races.

Based on our analysis of the races this year, we believe that the GOP could pick up 8 Senate seats. This would give them 49 Senate seats (out of 100), assuming that none of the GOP incumbents or open GOP seats flip to the Democrats. Additionally, we see 4 more Democratic seats that, with the right candidate, could flip to GOP, as the Democratic incumbents in those states are not polling very strongly right now.

Regardless of what happens, there are three more things that Senate Democrats need to consider: if the GOP were to get close enough to 50 votes, there is still the possibility that Independent Joe Lieberman of Connecticut may decide to join the GOP, or even caucus with them. Plus, Robert Byrd (D-West Virginia) is currently 92 years old. Assuming that he can even make it to his 2012 re-election race (when he will be 94), would he even want to run for another term ? Finally, in 2012 and 2014, those Democrats elected in the 2006 and 2008 landslides have to face the voters with the Christmas Eve healthcare vote on their records.