First, let's pick some probabilities out of the air like Al Gore mentioning that there's a 75% chance of there being no Arctic ice in six years. For the sake of argument, say that if John J. Miller considers it a "likely retention", then the party retains 90% of the time. If he considers it "leaning retention", then the party retains 75% of the time. And if he considers it a toss-up, it's a 50/50 proposition. In that case, his breakdown gives us:
- 4 GOP seats are "likely retain"
- 3 GOP seats are "leaning retain"
- 8 seats are "toss-ups"
- 5 DEM seats are "leaning retain"
So assuming independence, it's a simple matter to calculate the probability of different senate compositions after the 2010 elections. And without further ado, it looks like this:
- 21% chance that the GOP ends up with 39 or fewer seats
- 17% chance that the GOP ends up with 40 seats (same as today)
- 61% chance that the GOP ends up with 41-45 seats
- 1% chance that the GOP ends up with 46 or more seats
The bad news for the GOP is that of Miller's 20 "interesting" races, half of them are currently owned by the GOP. Naturally it would be better for them if their races were safe and all the DEM-controlled seats were in play. The worse news is that there's at least one chance in five that, even with the favorable poll numbers we're currently seeing, the GOP could drop even below 40, and two chances in five that they go no higher than 40. That would keep the filibuster off the table (although, as we've seen with health care, corraling 60 senators can be harder than it might be, especially in the teeth of countervailing public opinion).
The good news for the GOP, of course, is that there are three chances in five that they pick up some seats.
Take this analysis with liberal doses of salt and any other spices you happen to come across. Things are looking moderately up for the GOP, but there's a lot of work to be done before next November.