Jay Cost, a brilliant young political scientist, explores election myths surrounding the 2006 election. In 2004 he produced horserace blog which proved to be the most accurate in predicting the outcome of the 2004 election. 
Here's a sample, but I strongly urge you read it all. 

First, even if the Democrats could rally around a set of issues, they could not take the House. The national trends do not favor it. The economy is too strong and Bush is not sufficiently unpopular. Democrats are not capable of making Bush more unpopular, and certainly not interested in weakening the economy. Further, the number of open seats does not favor it. 95% of House incumbents are running again, and the reelection rate of incumbents in the last three cycles has averaged 99%. Democrats cannot undo what is one of the most important, yet least appreciated, secular trends in American politics: the movement toward perfect incumbent retention. Further, the tight alignment of the electorate does not favor it. 93% of Republican members of Congress are in districts Bush won. What kind of issues could the Democrats put forward that could win red districts without losing blue districts?

Second, the Democrats are structurally incapable of unifying. I find it fascinating that people on both the left and the right blast the Democrats, even going so far in some instances to make moral critiques of the party leadership. The argument seems to be that the Democrats could unite around something, but due to either a lack of vision or a lack of willpower, they have been unsuccessful.

The intuition behind this is that the 'normal' state of an American political party is unification. The Democrats themselves used to be unified, so the logic goes, and their lack of unity is their principal problem and a moral failing. In actuality, nothing could be further from the truth. American political parties are generally disunited, and the Democratic Party has been particularly disunited for quite a while. FDR Democrats have been a majority party for nearly 80 years; during that time, they have been a relatively loose affiliation of individuals who are tied together sometimes by issues, sometimes by history. Prior to Roosevelt, Democrats were more united, but they were also the minority party.

Today's pundits seem to demand a kind of programmatic, comprehensive unity — a new Democratic ideology that unites the most diverse members of the party, from San Francisco's Nancy Pelosi to Montana's Brian Schweitzer to Massachusett's Ted Kennedy to Arkansas's Mark Pryor. In other words, they want to get rid of the FDR Democratic Party, return to the William Jennings Bryan Democratic Party, but still keep majority status.

Clarice Feldman   3 14 06