Reasons why I think a socialist movement never broke through in the US.
1) Abundance of land and the earliness with which white workers got the franchise.
Most white Americans had the right to vote by 1840, and some states had given it much earlier than that. At any rate because of the abundance of the land the property requirement wasn't as prohibitive as in Europe. Since voting rights were acquired before industrial labor became widespread, this meant that organizations of industrial workers didn't have the impetus to organize on behalf of their class. In Europe, working class men only got the right to vote in the 20th century. Parties of the working class mobilized and organized to expand their rights. Whereas in America the working class was easily co-opted into the "populist" agitation of pro-system parties like the Jacksonian Democrats, or later they basically supported the agrarian and middle reform parties like the Populists. Furthermore, the 'feudal' tradition gave Europeans a stronger sense of class consciousness. Whereas America has always had this "frontier" tradition where people can settle unoccupied land and be independent.
2) The inequality within the working class itself and the development of a 'labor aristocracy'.
Within the working class itself, the people who dominated the early trade unions were the skilled workers unions of the AFL, while most workers were unskilled and very often immigrant labor. This combined with the fact that America at the end of the 19th century became an imperial power and therefore was able to extract superprofits from their colonial possessions, meant that the bourgeoisie could effectively "pay off" the upper section of the working class, making the latter content with their *middle class* lifestyle and resentful of the unskilled laborers who might undercut it. The steady flood of immigrant labor led to inevitable classes on issue of race and ethnicity. Ethnic homogeneity has, unfortunately, been a cornerstone of holding together many of the European welfare states, I must say.
3) Finally and perhaps most importantly is the unparalleled power of the American bourgeoisie. American monopoly capitalism was enormously strong at the time when the working class was starting to awaken to class consciousness, in the late 1800s. We all hear about the "trusts" and big corporations of that time period like Standard Oil, etc. Monopoly capital was able to wage savage *class warfare* against radicals and trade unionists with their private security forces, state troops, and strikebreakers.