A close look at the Senate polls suggests that they are likely understating the probability of Republican victories. Most seem to be under-sampling either Republicans, independents, or both. As a result, in 10 of 12 key Senate races, the Republican candidate’s likelihood of winning appears to be greater than what the polls are registering.To be sure, such conjectures are as much an art as a science.  But this much we know: 

First, both major parties’ ranks have thinned somewhat from 2004, while the pool of independent voters (Tea Party or otherwise) has expanded. Rasmussen shows 32 percent of voters now identifying themselves as not being a member of either major party, up from 24 percent in the fall of 2004.  That year, exit polling showed that 26 percent of voters were not affiliated with either party, and that number rose to 29 percent in 2008. It is likely to rise further.