From this article in the Economist:
[Californian] voters, moreover, have over time “self-sorted” themselves into highly partisan districts … The result is that elections are won during the Republican or Democratic primaries, rather than in run-offs between the two parties. This makes for a state legislature full of mad-eyed extremists in a state that otherwise has surprising numbers of reasonable citizens. … Because the Republicans are in a minority in the legislature, they have no sway until budget time, when they suddenly hold veto power thanks to the two-thirds requirement. Because in the primaries they have run on extremist platforms against other Republicans, they have no incentive to be pragmatic or moderate, and tend simply to balk.
With a little search and replace, this could easily describe Northern Ireland. 
(Thanks, Ed!)
