From The Marston Chronicles
To state the obvious, an open seat is when an incumbent decides not to run for re-election either just to retire on the fat pension provided to folks in Congress or to run for higher office. What an open seat does is make that seat available for pickup by the opposing party. We are coming up on a midterm election in 2010 which makes an open seat much more vulnerable. As was explained in Will the GOP Regain Control of the House?, the Republicans are about to pick up a bunch of seats anyway, because that is almost always what the opposite party of the one holding the Presidency does in a midterm election. An open Democrat seat is a golden opportunity for the Republicans to pick up a seat that would otherwise would be tough or downright impossible.
To illustrate what we mean lets take a look at what happens in the four Democrat districts where the seat is now open before and after it became open:
To state the obvious, an open seat is when an incumbent decides not to run for re-election either just to retire on the fat pension provided to folks in Congress or to run for higher office. What an open seat does is make that seat available for pickup by the opposing party. We are coming up on a midterm election in 2010 which makes an open seat much more vulnerable. As was explained in Will the GOP Regain Control of the House?, the Republicans are about to pick up a bunch of seats anyway, because that is almost always what the opposite party of the one holding the Presidency does in a midterm election. An open Democrat seat is a golden opportunity for the Republicans to pick up a seat that would otherwise would be tough or downright impossible.
To illustrate what we mean lets take a look at what happens in the four Democrat districts where the seat is now open before and after it became open:
| State | District | Incumbent Democrat | 2008 Margin | McCain Margin | Pelosi Health Care Vote | Took Seat | Takeover Probability |
| Kansas | 3 | Dennis Moore | 16.78% | -3% | Yes | 1998 | 49.6% |
| Kansas | 3 | Open | #4.78% | -3% | 2010 | #74.2% | |
| New Hampshire | 2 | Paul Hodes | 15.01% | -13% | Yes | 2006 | 49.9% |
| New Hampshire | 2 | Open | #7.10% | -13% | 2010 | #65.9% | |
| Louisiana | 3 | Charles J. Melancon | No Rep | 24% | No | 2004 | 62.8% |
| Louisiana | 3 | Open | #0.50% | 24% | 2010 | #97.8% | |
| Pennsylvania | 7 | Joseph A. Sestak Jr. | 19.19% | -13% | Yes | 2006 | 41.5% |
| Pennsylvania | 7 | Open | #12.76% | -13% | 2010 | #54.4% | |
| Tennessee | 6 | Bart Gordon | No Rep | 25% | No | 1984 | 20.9% |
| Tennessee | 6 | Open | #9.30% | 25% | 2010 | #74.1% | |
| Tennessee | 8 | John S. Tanner | No Rep | 13% | No | 1988 | -4.3% |
| Tennessee | 8 | Open | #24.78% | 13% | 2010 | #38.9% | |
| Washington | 3 | Brian Baird | 28.03% | -8% | Yes | 2008 | 25.4% |
| Washington | 3 | Open | #9.32% | -8% | 2010 | #63.1% |
Now you can see what a difference an open seat makes. Kansas 3 and New Hampshire 2 have gone from slightly less than an even chance to good bets for the Republicans. Louisiana 3 has gone from a good bet to an almost certainty. Pennsylvania 7 has gone from a possibility to a fair chance. Tennessee 6 has gone from the longest of long shots to a fair chance. Tennessee 8 has gone from impossible (a negative probability) to a poor chance. Washington 3 has gone from a long shot to a good bet.