Why are US politics so far to the right when compared to other westernized countries?
As I recall discussing this in political science classes years ago, here are a few factors no one has mentioned yet.
1.) A strict winner-take-all electoral system which has become a two-party system. European democracies have parliamentary arrangements which allow multiple parties in the national legislature. This makes it much more possible for "outsider" parties to influence legislation, build a track record, form coalitions, and leverage these gains into major-party status.
2.) The Senate. The U.S. gives the same number of Senate seats to states with smaller, rural populations as it does to states with larger, urban populations. People in rural areas tend to be more conservative, their attitudes of independence and isolation are adaptive in such economic circumstances, and their regional cultures tend to encourage individualistic attitudes while discouraging recognition of "Eastern" or "Northern" contributions to their quality of life. Their electoral power is magnified beyond their true numbers, putting a break on social democratic legislation.
3.) Lack of a strong socialist movement. European countries in the late 19th and early 20th centuries had large socialist movements. They also had smaller territories to organize in on their national levels. The U.S. electoral system made it harder for socialist parties to win votes and seats, so they didn't have much chance to build on a track record of reforms. Meanwhile, their issues were taken by the two major parties, channeling movement support to these parties in stead.
4.) Slavery. I think that having slavery, then Jim Crow and other racist laws during this time, seriously divided working class Americans. I recall the Populist movement of the late-19th century, and the union movement, being split over issues of race. Meanwhile, I get the impression that the more homogeneous societies of each of the European countries offered less of an opportunity to divide socialist and related movements along cultural lines. Perhaps European posters could clarify this, especially since many European countries were not ethnically homogeneous even 100 years ago.
5.) Religion and myth. There is a lot more religiosity, specifically Christian, in the United States, which tends to be a conservative force. Not always, of course, as we see with Quakers and the Catholic Worker movement, for example. But the main religious movements have tended toward the right, and those people usually vote. They backed out of politics a bit after the Scopes Trial embarrassed them, which might have helped make room for the New Deal. But they've come back since. They always do.
Meanwhile, in 19th century Europe there was a lot more anti-clerical sentiment during their democratic revolutions. The U.S. experience may actually derive from separation of church and state, while the European experience may derive from the ancien regimes' fusion of same. Is that irony?
You should also consider American exceptionalism, which is, as I recall, derived from 17th century notions of the Puritan Separatists. There is a sense that "America" is already good enough simply because it is already accepted that it is the shining city on a hill. I don't think any other countries have quite this kind of myth, certainly not Europe since that's where people were leaving
from. They already knew the grass wasn't green enough there.
6.) The notion of "Americanism". This is a tool that has been used for a long time to police the borders of acceptable political discourse in the U.S. In one sense it is valuable, in that it has provided a common bond for a diverse nation of immigrants. We're Americans because of our ideas about how a society should be governed, and not because of Old World ethnic, linguistic, or geographical identities.
However, this way of thinking can also used to proscribe any policies or practices that are or can be made to appear contrary to established tradition and national conformity. A smaller country without so many different established traditions might be easier to build some consensus in. Also, any idea that is associated with a hated out-group has a difficult time even getting a hearing here, and it just so happens that socialism and social democracy have been successfully associated with Jews (seen as greedy and not connected to the land), Europeans (seen as decadent and arrogant), and intellectuals (seen as impractical and arrogant).
Other: Sheer size, combined with a large population, may have something to do with it. This makes the U.S. harder to organize than a smaller country like Sweden or a less-populous one like Canada.
There may also be a cultural element of hyper-individualistic distrust of the Other derived from 17th century Scots-Irish culture, and the commercial cultures of New England and the mid-Atlantic state. See David Hackett Fischer on the Borderers. But this view is controversial.
I've also wondered if the total devastation of Europe during World War II contributed to the development of social democratic politics. Even though much of West Germany was occupied by the U.S. after the war, and they influenced the German constitution, West Germany still ended up more to the left than the country which didn't lose as much of its infrastructure. Could we also say that the defeat of Nazism and fascism allowed a sudden return of the movements they had been suppressing?
