I have been reading Aristotle's Politics and came across a passage relevant to the Eliot Spitzer scandal currently making the news. While discussing democracies in Ch. 4 of Book VI, Aristotle makes the following point:
Freedom to do exactly as one likes cannot do anything to keep in check that element of badness which exists in each and all of us. Hence it is most important to ensure that in constitutions this most valuable of principles shall be observed - government by good men free from error without detriment to the people at large.
A fundamental principle of democracies is liberty - the freedom to do as you like. In other constitutions discussed by Aristotle (oligarchy and monarchy, for example), behavior is more strongly constrained by law (including the behavior of the rulers, in good oligarchies and monarchies.) So it is not as critical that men be virtuous in those constitutions, because the law acts as a check on their vices. A state can get by with a mediocre King if the King is constrained by law regarding the sort of mischief he can make, or the sort of trouble he can get himself into.
But in a democracy, since the law does not act as a restraint on vice (or not as much as it does in other constitutions), those elected to power do not experience law as a check on their vices. What then prevents the government from descending into self-serving corruption? Only the good character of the government officials themselves. The restraint must come from within them rather than from without.
Thus the apparent paradox that in a democratic republic like ours, where individual vice is not generally a subject of the law, it is even more important to insistent on the virtuous character of public officials, and why it is entirely appropriate for us to toss the likes of Eliot Spitzer or Bill Clinton out of office.