Certainly Democrats can try to comfort themselves with the Wall Street mantra that "past performance is no guarantee of future results." But as they recover from a troubling 2009 election season, the party in power in Washington faces a lot of reasons for concern about the 2010 horizon. As Larry Sabato, a political scientist at the University of Virginia, explains, "[President] Obama is proving in this election that he can't transfer popularity." What's more, historical patterns suggest that the party of a sitting President, especially one with dipping approval ratings, tends to get hurt in off-year congressional elections. At stake is nothing less than the Democratic majority in the House and the ability to ward off filibusters in the Senate — not to mention executive control of many key states. If things go as badly as some now expect, Obama could see his legislative agenda run aground after less than two years in office.
Here is a look at the 10 elections that have Democrats most concerned: