The obsolete moderate.

"It all comes down to the fact that moderate Republicans aren't really moderate; they're Republicans." -- Steve Benen, The Carpetbagger Report

They can repeat "moderate," "less partisan," and "more centrist" all they want; at the end of the day, they're still an "R" and thus will serve to maintain the current power structure in Congress -- where all that truly matters is the number of R's vs. D's. The GOP status of Chafee and Snowe is what tips the power scale, regardless of their good, moderate intentions on any issues.

Paul Krugman wrote a column about this subject weeks ago. In another year at another time, moderate Republicans were always welcomed as they helped to keep the party from drifting too far in one direction. However, any such days are long gone as the extremely divided and partisan nature of Congress dictates that party membership means EVERYTHING, whereas a given politician's personal views on certain issues is almost meaningless as ultimately the few puppetmasters at the very top are going to make all the decisions.

In short, the numbers have it. Period.