Historically, it's common for the party in control to lose congressional seats in non-Presidential election years. But that is not the whole story, I think.
Why should they be re-elected? What have the accomplished? It's not hard to see whose interests they have been serving in the past two years, and for average voters, it isn't them. I remember well that after George Bush's people stole the election in 2000, Democrats fell all over themselves trying to help that man with his outrageous plans --- rewarding the wealthy with huge tax cuts, invading Iraq, knocking down governmental regulation of the banking and finance industries, borrowing billions from foreign countries. Now that they are in power, what have the accomplished? Whose interests have they served?
So, let me ask: Why should we bother to vote Democratic?