The only actually existing political parties in the US are the Dems and the Reps. All third parties have no chance whatsoever of attaining the "immediate aims" or "enforcing momentary interests of the working class " at the federal or state levels , because third parties are not voted for by the working class, the 99%, our class. In terms of US historical specifics, third parties have digressively gotten smaller and smaller percentages of the vote for 100 years or more; Bull Moose , Socialist, CP, Progressive, Nader. There is a clear trend for third parties becoming obsolete, an objective political scientific phenomenon in the US political culture that Communists cannot ignore.
Marx and Engels explicitly say Communists ally with bourgeois parties in the Manifesto :
"Communists fight for the attainment of the immediate aims, for the enforcement of the momentary interests of the working class; but in the movement of the present, they also represent and take care of the future of that movement. In France, the Communists ally with the Social-Democrats(1) (1) The party then represented in Parliament by Ledru-Rollin, in literature by Louis Blanc, in the daily press by the Réforme. The name of Social-Democracy signifies, with these its inventors, a section of the Democratic or Republican Party more or less tinged with socialism. [Engels, English Edition 1888] * * *
against the conservative and radical bourgeoisie, reserving, however, the right to take up a critical position in regard to phases and illusions traditionally handed down from the great Revolution. In Switzerland, they support the Radicals, without losing sight of the fact that this party consists of antagonistic elements, partly of Democratic Socialists, in the French sense, partly of radical bourgeois. In Poland, they support the party that insists on an agrarian revolution as the prime condition for national emancipation, that party which fomented the insurrection of Cracow in 1846. In Germany, they fight with the bourgeoisie whenever it acts in a revolutionary way, against the absolute monarchy, the feudal squirearchy, and the petty bourgeoisie"