A basic question now is how many of the Democrats up in 2010 represent “low-hanging fruit” ripe for Republicans to harvest. In 1994, there were plenty of Democratic congressional seats ready for the plucking, especially in the South. The Democrats ended up losing more than 50 House seats that year, along with eight Senate seats, and descended into minority status in Congress for the rest of the Clinton presidency.

As then, the current Democratic majority in Congress was built by winning seats in normally Republican terrain. But many of the current crop of Democratic newcomers are conservative to moderate, carefully recruited to match the ideological mainstream of their districts. They are not necessarily sitting ducks.

Ultimately, which party prevails in 2010 will depend on who votes. Midterm turnouts tend to be smaller, older and whiter in composition than those for a presidential election. Even small changes in the midterm electorate can have a large bearing on the outcome.

In President George W. Bush’s first midterm election in 2002, slightly more Republicans than Democrats turned out to vote, and the GOP picked up seats in both the House and the Senate. When Democrats won control of Congress in 2006, the situation was reversed: Slightly more Democrats than Republicans cast ballots.