According to 538, the democrats are going to lose in 2010. They will lose roughly 4-6 net senate seats and about 30-60 house seats. There is a realistic chance the house will go to the GOP.
So on the surface this is horrible. But long term, it might actually be good.
Demographics in the US are shrinking the GOP and growing the democratic party. The GOP is a party that more or less excludes the economically insecure, non-married, non-christian, non-white, non-conservative.
However all these groups are growing dramatically. Nonwhites went from 13% in 1992 to about 26% in 2008, and will reach about 34% in 2020.
People born after 1978 tend to be economically and socially liberal. They went democratic pretty hard starting in 2004 (the dem advantage was up to about 34 points in 2008). By 2020 they will make up nearly 1/3 of the electorate, up from about 20-25% now.
We are becoming more and more secular. The % labeling themselves non-religious goes up about 5-10 points every generation.
All of these assumptions rest on the assumption that voting habits will follow demographics. That isn’t guaranteed. About 50 years ago women leaned GOP and southern whites were heavily democratic. Now women lean democratic while southern whites are republican.
But if the GOP wins big in 2010, they will likely take it as a referendum on the tea party and hardline conservatism, and feel those ideologies are what got them reelected (rather than fear of 1 party rule, or lack of action by the dems on the economy, or lack of courage, discipline and principal on the part of the democrats, etc). So the GOP will move further to the right. They will become more radical and obstructionist, which will drive even more people out of their ranks. More laws like the one in Arizona will alienate latinos. More pro-life legislation will alienate women. More indifference to economic issues of the working class will alienate the insecure. More creationism, climate change skepticism and bad math (tax cuts + endless war + no meaningful spending cuts = balanced budget) will alienate professionals and intellectuals. As a result they will alienate these people (women, professionals, young people, non-whites, the economically insecure) etc. even more than they already have. And these groups will keep growing while the GOP base (elderly white christian conservatives) keeps shrinking.
By the middle of the next decade, the GOP could truly be a minority party. After winning in 2010, they push too far to the right and end up alienating the public all over again (like they did in 2005).