Marx & Engels' "Address of the Central Authority to the League, March, 1850”:

[T]hat everywhere worker’s candidates are put up alongside the bourgeois democratic candidates, that they are as far as possible members of the League, and that their election is promoted by all means possible. Even when there is no prospect whatever of their being elected, the workers must put up their own candidates in order to preserve their independence, to count their forces and to lay before the public their revolutionary attitude and party standpoint. In this connection they must not allow themselves to be bribed by such arguments of the democrats as, for example, that by so doing they are splitting the democratic party and giving the reactionaries the possibility of victory. The ultimate purpose of all such phrases is to dupe the proletariat. The advance which the proletariat party is bound to make by such independent action is infinitely more important than the disadvantage that might be incurred by the presence of a few reactionaries in the representative body. If from the outset the democrats come out resolutely and terroristically against the reactionaries, the influence of the latter in the elections will be destroyed in advance.