THE NATURAL COMPOSITION IS 60-40.

Looking to 2012, but in the Senate (DAVID M. HERSZENHORN, 10/30/10, NY Times)

The numbers are stark. Democrats will be forced to defend 24 seats in the 2012 election, including those of two independents aligned with them, compared with just 9 seats for Republicans.

Even those numbers do not fully reflect the steep challenge Democrats will face. Many of the Democratic senators up for re-election hail from battleground states, including Sherrod Brown of Ohio, Bob Casey of Pennsylvania, Claire McCaskill of Missouri, Bill Nelson of Florida and Jim Webb of Virginia. Others from traditionally Republican-leaning states may have it even harder, including Kent Conrad of North Dakota, Ben Nelson of Nebraska, above, and Jon Tester of Montana.

The sole Republican up for re-election in a traditionally Democratic state will be Scott Brown of Massachusetts.