Progressive Punch has just announced the addition of a new tool for rating members of Congress, which should prove especially useful in getting a fix on different Democrats. It's called a "Chips Are Down" score and has just been calculated for the current congressional session.
The votes used to calculate the scores in the "Chips Are Down '07-'08" column are a subset of the overall votes that qualify according to the Progressive Punch algorithm described above. They show the impact that even a small number of Democrats have when they defect from the progressive position. These are votes where either progressives lost or where the progressive victory was narrow and could have been changed by a small group of Democrats voting differently. The definition of a vote where progressives lost is one where a majority of the progressive cohort (see list below) was on the losing side of the vote. Narrow progressive victories are defined as votes in which progressives won by 20 votes or fewer in the House (so a shift of 10 votes from one side to the other would have changed the result) or by 6 votes or fewer in the Senate (so a shift of 3 votes from one side to the other would have changed the result).