Probably the best measure of a candidates ideology is the DW NOMINATE score. It takes a wide variety of position measures into account, including both roll calls, party loyalty, and non-vote position papers. If you look at the embedded graph, you will see that there are clusters that pretty well define the politicians involved, but there is a coherence to the various parties.
McCain, in particular, is by just about any measure, a maverick. That said, he isn't alone. In The Measure of a Maverick, Henry Brighouse writes:
Under this definition, John McCain is very definitely a maverick. Indeed, he’s the seventh most mavericky Senator since 1877. However, he isn’t the most mavericky Senator in recent history; that honour goes to Lincoln Chafee, who comes in at number three. Also, McCain-ites who want to embrace this result should note that it is based on the same kind of measures of ideology (DW-Nominate scores) that have been used to show that Barack Obama, contra the National Journal and Republican mythology, is not (for better or worse) the most liberal Senator by a significant stretch.
There are ways of measuring this stuff after all.
McCain's exact scores are as follows:
- Rank = 67
- First Dimension DW-NOMINATE Joint Scaling
- Second Dimension DW-NOMINATE Joint Scaling
- Total Choices this Congress
- Geometric Mean Probability
- Proportion Correctly Classified
112 ARIZONA MCCAIN 0.380 -0.657 -101.64865 387 0.769 0.884