Most historians have a very strong candidate — James Buchanan, our 15th chief executive (1857-1961), the president just before Abraham Lincoln. In fact, there is a new biography out entitled Worst. President. Ever. by Robert Strauss.
Why was he so bad? Despite a glittering resume — the Pennsylvania legislature, the U.S. House and Senate, minister to Russia and Great Britain, and he had run for president twice before — he was unsuited to the governmental functions of the office. Consequently, he bungled the major crises that directly led to the Civil War. On the other hand, he was the best party-giver of his era.
There is a good snapshot of James Buchanan entitled “The Partying President” at Smithsonian VIP (http://links.sicirculation.mkt6348.com/servlet/MailView?ms=Mjc2MjMwNjES1&r=ODU4MDk3OTA1NDUS1&j=OTY0MTI4ODc3S0&mt=1&rt=0).
The photo came from Amazon.com.