Florida, with three Republican seats in play, exemplifies most of the factors that have improved Democrats' chances.

Two seats changed parties, both Republican seats that switched to Democrats.

Two of the Democrats took Republican seats in 2006, and were at risk during the 2008 election.

Democrats must win six Republican seats to regain a Senate majority, meaning they would have to win nearly every close race.

Twenty-one Republican seats will be open, compared with 12 Democratic seats.

That puts four Republican seats in play.

Democrats must pick up six Republican seats to regain control of the Senate, a formidable task.

In 1992, the year of maximum peril for the Democrats, only 14 Republican seats will be at issue.

Democrats need to pick up 15 Republican seats to take control.

There are 15 Democratic and 18 Republican seats up next year.