> * * * The constitutional/federal system didn't
> prevent the Communist Party from electing a
> Congressman, Vito Marcantonio, right down to
> the McCarthy period, . . . . [who] once elected,
> . . . failed to act independently of the Democrats.
Throughout his congressional career, Marcantonio was endorsed by and ran on the Republican line, several times in addition on the Democrat line, albeit (later on) also on the in part Communist supported ALP line.
Whether he did not act "independently of the Democrats" is substantially debatable, unless one defines the (very) substantial (especially but hardly only: left-wing) labor union support and, then even more important in his district, individual union member support as "Democrats".