Pressure groups in US Politics is the topic that can provoke the worst answers from students. In the blind panic of an exam they fall back on their AS level knowledge and produce an AS level essay. Part of the reason for this is lack of understanding of the differences in US groups and how they work.
This article is fabulous evidence for the influence that conservative groups wielded in the last Congress, with the government shutdown being attributed to some of them, and their fall from grace currently. The Republican Party seem to be going to greater lengths to distance these groups from the Party; unsurprisingly, perhaps, given the unpopularity of the shutdown itself. You should take the names of groups, which you can use in your essays, from this article, as well as actual actions they have carried out. This should avoid the dreaded argument that, ‘the NRA lobbies Congress against gun control’ – whatever that means!