But, you may ask, if the two departments [i.e., federal and state] should claim each the same subject of power, where is the common umpire to decide ultimately between them? In cases of little importance or urgency, the prudence of both parties will keep them aloof from the questionable ground; but if it can neither be avoided nor compromised, a convention of the States must be called to ascribe the doubtful power to that department which they may think best.
Thomas Jefferson