James Buchanan. he put up the biggest stint about politcal corruption, yet he himself was invloved in such coruptioon as:
1. Giving a Philidalphia shipping company a government contract so that they would donate money to one of Buchanan's friends reelection to Congress.
2. Attempting to emebezel the $25 million that Congress approrpiated to Buchanan's Administration to buy Cuba.
3. Brought in over 300 illigal immigrants to be illegaly naturalized so they could vote for Democratic Candidates in the 1858 Congressional Elections.
And the list goes on...
Many people think that Buchanan backed out of the 1860 race because he didn't like the looks of the future of the slavery conflict, and that is probably true. But there is also the likelihood that he was afraid of being found out on some of these issues.