Here's some R to get started. 

The next step is going to take some work, I think. In the end, we'll need to see some snapshots at each stage and some more detailed analysis at each point instead of the cumulative strength of ties. For example, there may be 80 congressmen with a small (.1) preference for an issue and 19 with a strong preference against it (-1) and the cumulative fit will be ((80 * .1) + (20 * -1)) = (8 - 19) = -11; but that wouldn't represent the prospects of a vote on that issue very well.