Gads this stuff frustrates me. First let's get some definitions out of the way. I generally avoid Wikipedia on some of these because it can be rather politicized itself, but at least the first sentence of the Fascism article seems on point:
Fascism is an authoritarian political ideology (generally tied to a mass movement) that considers individual and social interests subordinate to the interests of the state or party.
Socialism:
Socialism refers to a broad array of ideologies and political movements with the goal of a socio-economic system in which property and the distribution of wealth are subject to control by the community[1] for the purposes of increasing social and economic freedom, equality and cooperation. This control may be either direct—exercised through popular collectives such as workers' councils—or indirect—exercised on behalf of the people by the state. As an economic system, socialism is often characterized by state, worker, or community ownership of the means of production, goals which have been attributed to, and claimed by, a number of political parties and governments throughout history.
And... for the sake of completeness, Bolshivism:
The Bolsheviks believed in organizing the party in a strongly centralized hierarchy that sought to overthrow the Tsar and achieve power. Although the Bolsheviks were not completely monolithic, they were characterized by a rigid adherence to the leadership of the central committee, based on the notion of democratic centralism. The Mensheviks favored open party membership and espoused cooperation with the other socialist and some non-socialist groups in Russia. Bolsheviks generally refused to co-operate with liberal or radical parties (which they labeled "bourgeois") or even eventually other socialist organizations, although Lenin sometimes made tactical alliances.
Now wiser men than I have described the political spectrum as a horse-shoe with Fascism and Communism at the tips, curved inwards towards each other. That's an apt description and tells us a lot about the ideology's histories. Facism and Bolshivism, while both totolitarian systems in Europe before the Second World War, had entirely different origins - both politically and ideologically. Fascism grew out of extreme nationalism, a scattered set of peoples with no real shared national identity who sought to create that identity in law, government, and - in the case of Nazi Germany - Genocide. From a set of scattered and independent states, unity in the person of a charismatic leader was all important.
Bolshevism grew out of a reaction to authoritarianism [edit: and aristocracy] and a profound envy of the power of industrial Europe. Casting off both the Tsarist government and the Provisional Government under Krensky, the Bolsheviks sought the party apparatus that marked the great powers of Europe but were unwilling or unable to compromise in their ideology with competing parties. From this grew the one-party system of Soviet Russia, at once very similar to but entirely different from the Fascist movement of Italy and Germany.
This is key historically speaking. Fundamentally Germany and Russia were not friends. Hitler's writings in Mein Kamphf demonstrate that, even years before he rose to power, Hitler anticipated a coming war with Russia. Though the two turned to systems designed to empower them militarily, they did so as natural enemies from opposite and entirely unrelated ends of the political spectrum.
Why am I going into such historical detail here? Because it is vital that we establish that Socialism is neither the foundation of Bolshevism nor Nazism. The Nazis co-opted the word "Socialism" and while Marx predicted that communism would follow Socialism, Lenin and Stalin's Frankenstein monster of a political system bore no resemblance to anything Marx discussed.
So what of American Fascism? We have conflated, unfortunately, the notions of Fascism and Nazism for reasons that are fairly obvious. The result of this is that Fascism is a "bad word" in American politics, even when appropriate. Regardless, the Bush administration certainly displays the hallmarks of a fascist party -- the manipulation of the media, close alliances with corporate interests, the marginalization of dissent through the impugning of patriotism, nationalism, an advancing security state, centralization of executive power, and yes - even the identification of a subversive "other" to justify these encroachments upon liberty.
But note how Fascism's hallmark is the encroachment of government upon the
personal whereas socialism's hallmark is the government's interference with the
social. Therein lies the difference. Socialism is about
social government. Fascism, from the Latin "fasces", refers to the implements of state authority - and specifically the state's rights to punish and kill.
The two are almost night and day.