And how do you know that the conditions are favorable a year and a half out?
It's true, there's some guesswork in that. I factor that into my percentages. I'm basing it on the fact that every party gets a honeymoon, and that the severity of the economic crisis, the duration of Republican control, the Republican Party's current behavior, and Obama's strong political skills point to the honeymoon carrying through long enough to prevent more than a regional backlash in 2010. I do not think 2010 will be like 2006 or 2008, and that Republicans will net seats in the House and that a flawed senator like Chris Dodd is in real trouble whereas he would have survived in an "anyone but Bush" election like the last two. I think a moderately good Democratic year makes most Democratic senate candidates in Pennsylvania unbeatable, and that an average year still gives the Democrat an edge over Toomey because his views and past votes are not currently popular in the state, no matter how good a candidate he may be. I base this as I said before on my experience watching good Dems go down to passable Republicans in senate races that were simply not winnable for us.
You disagree in your assessment of where we're going and how swingy Pennsylvanian voters can be, and that's fine, this is just my assessment and we'll see soon enough how things shape up.