Add it up and you have 168 seats in which the current incumbent won with 67 percent or more of the vote. That's 38 percent of the entire House with virtually no concern about losing a general election.
Those numbers are even more remarkable when stood against the paltry group of seats that are genuinely competitive between the parties. In the 2012 election just 31 Republicans and 31 Democrats won their seats with 54 percent of the vote or less -- just 14 percent of the entire House.
In short: There are almost three times as many members elected with 67 percent or more as there are elected with 54 percent of the vote or less. Given that data, it shouldn't be surprising to anyone that the incentive to cooperate with the other side and find bipartisan solutions is almost nil.
Sure, there are lots of reasons for the shut down that go beyond raw politics. But, if you started that discussion with the gerrymandering of the country's Congressional districts to virtually ensure that one party will always win and add to it the prevalence of closed primary systems that reward running as far to the right or the left ideologically as possible, you'd be on the right track.