Why is there no socialist party in the United States?

Before considering the reasons why there is a distinct lack of left-wing parties in US politics, it is first necessary to define exactly what we mean by "socialist party," as it is not the case that a Socialist party and a social democratic party are the same thing; indeed, they represent entirely different approaches to the interventionist economic philosophy. Socialism refers to a desired outcome, the wish to fundamentally alter or negate the basic features of capitalism, sometimes displaying a militant or violent streak, whereas social democracy attempts to modify and reshape capitalism in such a way as to minimise the inequalities the market system brings about; in other words, to try to make capitalism more acceptable in terms of social justice. It is also an important distinguishing characteristic that not all social democrats see an inevitable end to capitalism in the future. Thus, given that most contemporary left-of-centre parties are based on the socialist democratic movement (e.g. New Labour, the market-friendly Parti Socialiste in France, and the German CDU-led coalition would all be correctly classified as social democratic parties as opposed to pure socialist parties), it is perhaps more correct to refine the above question to "Why is there no social democratic movement in the United States?" i.e. a parliamentary political party based around the working class voter.
Even with this distinction in place, there has still never existed such a movement in the United States. The reasons for this can be split into ideological and political, economic, and social factors.
Examining the historical development of social democratic movements in European countries, and then looking for similarities and differences in the USA's history may yield some answers. Generally, the socialist movement in Europe manifested itself during the transition from a laissez-faire attitude to the economy to the idea of organised capitalism; this occurred between approximately 1890 and the outbreak of W.W.I in most European countries (Britain was an exception to this rule, where socialism did not make a breakthrough until after W.W.I; reasons suggested for this include the beneficial impact of Britain's colonial status on the working class here, more pronounced than other colonial powers of the time). These movements rose out of strong trade union activism, which prompted the founding of political parties to represent the views of the working classes. Why did this not happen in the United States? The short answer is that the traditional views of socialists and social democrats were never held by more than a minority of American workers, and thus there has never been wide-scale support for a socialist party. What is different about the average American worker that would explain this?
Firstly, we must examine the economic reasons why socialism is not a popular doctrine among the blue-collar workers. The first one of these is the typical worker's favourable attitude towards capitalism itself. Contrary to most other countries, the working-class of America is generally enthusiastic and incredibly supportive of the idea of capitalism, because it provided for his material needs. This was the attitude that prompted mass immigration into the country. The integration of the worker into the capitalist society helped them identify with their employer, and fostered a sense of the businessman in the worker himself. Then, of course, whilst the system may not be working for them, it was working for others, and the dreams harboured by Americans for their children's prosperity encouraged their loyalty to the capitalist ideal.
Closely connected to this is the suggestion that the rewards that the capitalist system was able to provide to American workers ensured the suppression of radicalism. In looking at what they had, the workers were able to see that they were relatively affluent, and were certainly better off than their European counterparts. Such a level of affluence would prevent the rise of a social democratic movement. Sombert suggests that above a critical level of income, quasi-middle-class attributes emerged among the working class; again, this would hinder the development of any sympathies with socialism.
However, this theory is not as compelling as other parts of the argument. It is not clear that prosperity in a country automatically impinges on the fortunes of the left-wing movement; nor does affluence automatically mean that people will not be attracted to these views. This embourgeoisement theory failed critically to take into account the vast inequality in income that was present in both immigrant and American-born citizens, which meant that, although the average working-class wage was undoubtedly higher than the corresponding wage in any European country, there were many numbers of families on or below the poverty line. Conversely, there also existed a so-called aristocracy of labour. Thus, this argument is misleading in offering the impression that there was, or indeed is today, a universally affluent working-class in America.
It is also the case that there exist, or at least previously existed, greater opportunities for upward social mobility in the US. Workers can move up the social and economic ladder, and become entrepreneurs themselves. Even Marx admitted that there was a "flux of classes" in American society. This helps explain the typical worker's attitude to capitalism.
Furthermore, the attraction of the open frontier that existed in America until recently has been argued as being a factor in helping to reduce the militancy of the American worker. If they ever felt oppressed by a life of capitalism in the East of the country, they could "go west" and settle in the great expanse of the unexplored frontier. Unfortunately, this argument is inconsistent with the American worker's supposed innate love of capitalism, and so is not really convincing.
There is not only economic integration of the worker, but political and civic integration as well. The existence of universal suffrage almost from the beginning of the republic, and certainly well before the rapid industrialisation of the 19th century meant that a socialist movement could not have arisen to campaign for equal voting rights between classes. This is in contrast to other countries where the inequality in voting rights was a contributing factor in the founding of left-wing movements, where universal suffrage followed industrialisation. Again this integration can be said to have suppressed radicalism among the working class.
Perhaps the most important political factor that has prevented the growth of socialism, or indeed any third party in US politics, is the duopolistic nature of the party system. The power and reach of the Republican and Democratic parties have had similar repercussions that the existence of a duopoly in an economic market might have; namely, the erection of barriers that prevent any new entrants to the arena. Given that many third parties often campaign on only one issue, e.g. the environment or women's issues, it is not a tremendous difficulty for either of the main parties to adjust their position on that particular issue just enough to capture most of the third party's electorate, thus rendering it impotent.
Even if a party emerges that has a broad manifesto and is serious at attempting to break the mould, it still has to persuade voters to abandon their traditional voting habits, and this was a problem that was never really overcome by the socialist movement in the US. Political alignments and loyalties had had over a century to become entrenched before the attempt to introduce a socialist movement, and as a result these tendencies and preferences were highly stable. This persistent support for one or other of the main parties, combined with voters who are not psychologically disposed to break the voting habits of a lifetime means that it requires something special for a third party to become established.
It is only in times when either of the big two parties are in crisis that a third party has an opportunity to assert itself. The only time the Socialist Party in the United States had a significant impact was in the 1912 Presidential election, when the Republican party was split, and traditional party allegiances were in disarray. The majority of support for the Socialist Party came among the young, who weren't tied to one particular party, and those living in rural areas, where the party machines couldn't exercise control over the electorate. However, by the time of the next election in 1916, the two-party status quo had reasserted itself, and support for the Socialist Party declined. Thus, the lack of recurring fissures among the bourgeois parties in the US, as compared with other countries such as Germany, can help explain the bipolar party system and the difficulty of entry by new parties.
The failure of the Socialist Party can also be attributed to the circumstances surrounding the mass immigration into the US in the latter half of the last century. Once again, their assimilation into the political and economic structure, despite the poverty many found themselves faced with, prevented the existence of a permanent underclass that could have identified with, and formed the base of the support of, a socialist movement. Trade union hostility to these newcomers did not help the situation at all; the trade union at the time saw the immigrants as threats, and were self-oriented. Once again, the beliefs in both longer-term prospects and the capitalist society as mentioned earlier are important. The immigrants also had other reasons for not supporting any social democratic or socialist movement. Neither the political circumstances they were faced with in the large cities of the North East, nor their own private political views were conducive to their supporting a movement of this sort. This is because the acceptance of socialism is not a spontaneous action; instead, one requires education as to the nature of the system, backed up by appropriate leadership. Obviously this was not forthcoming in the cities, where the only education the immigrants were likely to receive was from their employers or local political leaders, who would in no way have espoused support for socialist doctrines.
This failure to win support among the immigrant population would prove costly for the Socialist Party. In short, in order to have a dramatic impact on the party system, it needed the support of the urban and immigrant vote. However, many potential Socialist voters from these areas, mostly Republicans, were unwilling to switch allegiances, fearing a Democrat victory. It is also surprising that the event that contributed a great deal to the rise of the Labour Party in Britain, namely W.W.I., did not have a similar impact on the fortunes of the social democratic movement in the US. However, the short-term successes of the party during the war, when it opposed America's intervention, did not continue after the armistice. Whilst Britain was shocked and underwent a series of social structure in the aftermath, the mood in America was very different; the late entry to the war did not fully impress its horrors on the American public, and thus she was left in a state of fervent patriotism, but with no war to fight.
This, combined with the successful Russian (and unsuccessful German) revolutions brought a feeling of fear among the middle-classes in the US that the same thing would happen in the US; thus the 1920s saw a period of repression of the Left from which the Socialist Party would not recover.
So far in this discussion, I have used the terms working-class and middle-class as if they are the definitive boundaries by which American society can be classified. However, the situation is far more complex than this suggests. In fact, it simply is not the case that Americans feel strong affiliation to any particular socio-economic grouping; rather, the predominant division is the question of ethnicity. The result of such division is quite simple; given that the term working-class encompasses many different ethnic groupings, each with its own view on and attitude to a particular issue, there has never been a working-class consensus that would form the base of a socialist or social-democratic movement. It is this, in concert with the economic, political, and social factors described above, that explains such an absence from the political arena in the United States.