Voteview blog has, not surprisingly, found that partisan polarization has increased, “almost entirely due to the movement of congressional Republicans to the right.” To a certain degree partisan polarization is due to the parties lining up based upon ideology far more than in the past. Previously there were conservative Southern Democrats but these are now Republicans. There also used to be a meaningful number of Republican moderates and even liberals. Therefore in the past it was possible to have groups crossing party lines agreeing on legislation.
An even more important factor in the current polarization is that the Republicans have moved much further to the extreme right in recent years while we have not seen an analogous movement to this degree by Democrats to the left (Some would argue that the Democrats have also moved to the right). The post concludes:
We have previously written about asymmetric polarization, arguing that the primary driver of contemporary partisan polarization has been the steady movement of congressional Republicans to the right. This trend appears to have continued through the 112th congress. House Republicans – despite a large majority earned in the 2010 midterm elections – have continued their rightward drift, adding more conservative members than moderate members. Senate Republicans also became a more conservative group in the 112th Congress, while Senate Democrats remained mostly ideologically static. Some of this phenomenon is attributable to the fact that Democrats – particularly northern Democrats – were already holding liberal policy positions in the 1960s. The “Great Society” programs enacted during the 1960s have appeared to represent the leftward edge of what is practically achievable in American public policy (for example, from an ideological standpoint, “Obamacare” is not more liberal than Medicare, enacted in 1965). Congressional Democrats have staked out this position and have mostly maintained it in recent American history. Congressional Republicans, on the other hand, continue to pioneer new ideological territory along on the rightward edge of American public policy. It remains unclear whether and how long this pattern can persist.
The statement that Republicans “continue to pioneer new ideological territory along on the rightward edge of American public policy” is a very tactful way to say that they have become bat-shit crazy.