"Now, if a publican is a tax collector, what is a republican?"

A republican (small "r") upholds the chimera of Strictly Limited Government (and its attendant light burden, Strictly Limited Taxation). He fancies himself a Constitutionalist, but grants his government the authority to interpret the very document designed to constrain its latitude to act. Surprising enough, those interpretations prove expansive, and Strictly Limited Government quickly degenerates into the kind of welfare-warfare statism now besetting the American public.

A Republican (capital "r"), as your question cynically suggests, favors twice the publicanism--and thus twice the welfare-warfare statism--as his small "r" counterpart. He offers a short cut to the same inevitable and tyrannical end.