Greed, stupidity, and sucking up to social strongfolks, according to this piece by Mike Lofgren, a former Republican staffer.
To those millions of Americans who have finally begun paying attention to politics and watched with exasperation the tragicomedy of the debt ceiling extension, it may have come as a shock that the Republican Party is so full of lunatics.
http://www.truth-out.org/goodbye-all-reflections-gop-operative-who-left-cult/1314907779
A couple of years ago, a Republican committee staff director told me candidly (and proudly) what the method was to all this obstruction and disruption. Should Republicans succeed in obstructing the Senate from doing its job, it would further lower Congress's generic favorability rating among the American people. By sabotaging the reputation of an institution of government, the party that is programmatically against government would come out the relative winner.
http://www.truth-out.org/goodbye-all-reflections-gop-operative-who-left-cult/1314907779
It is the apocalyptic frame of reference of fundamentalists, their belief in an imminent Armageddon, that psychologically conditions them to steer this country into conflict, not only on foreign fields (some evangelicals thought Saddam was the Antichrist and therefore a suitable target for cruise missiles), but also in the realm of domestic political controversy.
http://www.truth-out.org/goodbye-all-reflections-gop-operative-who-left-cult/1314907779
It should have been evident to clear-eyed observers that the Republican Party is becoming less and less like a traditional political party in a representative democracy and becoming more like an apocalyptic cult, or one of the intensely ideological authoritarian parties of 20th century Europe. This trend has several implications, none of them pleasant.
http://www.truth-out.org/goodbye-all-reflections-gop-operative-who-left-cult/1314907779
If you think Paul Ryan and his Ayn Rand-worshipping colleagues aren't after your Social Security and Medicare, I am here to disabuse you of your naiveté.[5] They will move heaven and earth to force through tax cuts that will so starve the government of revenue that they will be "forced" to make "hard choices" - and that doesn't mean repealing those very same tax cuts, it means cutting the benefits for which you worked.
