Who does the corrupting?

One of the most convenient bugbears of American politics is "the rich," a group which is apparently perpetually engaged in corrupting well-meaning civil servants, taking money from taxpayers in the form of corporate welfare, and all around screwing the populace over by manipulating government for nefarious purposes.

Does this happen sometimes?  Well yes, of course.  Corporate welfare is just as immoral and unconstitutional as handouts to the poor -- and far less sympathetic and understandable a cause.  In fact, as Ron Paul has explained,

It is not only bad economics to force working Americans, small business, and entrepreneurs to subsidize the export of the large corporations: it is also immoral. In fact, this redistribution from the poor and middle class to the wealthy is the most indefensible aspect of the welfare state, yet it is the most accepted form of welfare. [It] never ceases to amaze me how members who criticize welfare for the poor on moral and constitutional grounds see no problem with the even more objectionable programs that provide welfare for the rich.

And it goes without question that corrupt alliances between government and corporations or wealthy individuals are both wrong and illegal.  But the question must be asked:  Who does the corrupting?  Or, as Walter Williams puts it:  Who poses the greater threat?