Last month, we outlined the newest release of the Cook Partisan Voting Index (PVI), which measures the partisan lean of all 435 U.S. congressional districts. The data showed that Democrats made major gains across Northern Illinois, even in districts currently occupied by Republicans. The western suburban 6th District and Rockford-based 16th District, for example, each moved three points to the left, with the former losing its GOP-lean entirely.

Yesterday, Swing State Project took this analysis to the next level, rolling out their PVI/Vote Index, which compares the lawmakers' 2008 voting records against the PVI of their districts to identify who is overperforming or underperforming in Washington.  To measure the liberal or conservative lean of each lawmaker, Swing State used the well-respected DW-NOMINATE scores.

According to the data for Illinois congressional delegation, GOP Reps. Don Manzullo (IL-16) and Peter Roskam (IL-6) are among the 20 lawmakers whose voting records are more conservative than their constituentcies. As Swing State notes, both are "right-wing Republicans camped out in moderate districts."

Having followed both men's antics for a year now, we can't say we're surprised. Just last week, for example, the two sided with Wall Street's biggest banks and voted against the credit card reform bill that passed the House with overwhelming margins. 

Interestingly enough, two Illinois Democrats -- Reps. Bobby Rush and Dan Lipinski -- are among the most underperforming lawmakers in the country. Rush, the 83rd most liberal member, legislates the 12th most Democratic district in the country while Lipinski -- himself the target of a Democratic primary during the 2008 cycle -- votes routinely with the Democrat's conservative wing despite his district's solidly liberal composition.