From The Deep State, by Mike Lofgren, pg 231. This strikes me as a really important point: politicians are insulated from external pressures while nonetheless having their behaviour shaped all the more by internal pressures, driving a political polarisation which can seem prima facie like the intensification of politicisation rather than its diminuation:
Thanks to the scientific gerrymandering of House districts and the voluntary “social sorting” of people with similar political beliefs into the same zip codes, incumbents are roughly 96 percent safe in general elections. So it is highly unlikely that a Tea Party Republican will ever be defeated by a Democratic candidate in the general election. The Economist has pointed out that House members, both Democratic and Republican, are safer in their districts than the crowned heads of the European monarchies, who have had a higher rate of turnover through death or abdication. The only threat to an incumbent Republican is a primary challenger who stands even further to the right. Thus has ideology replaced money, by no means in all races, but in the contests for a crucial fifty or sixty seats in the House of Representatives.