He actually wasnt a terrible candidate. He made no serious errors (the 47% remark didnt cost him). In fact Id say he was the best losing candidate since Nixon in 1960. Which is why there is a Romeny push now.
The worst candidate of the past 50 years was probably Gore in 2000. More so than McGovern or Goldwater. Neither the GOP in 64 or Dems in 72 were going to win, so mine as well have a fun campaign with a purity candidate.
Gore by far was the worst.
He lost an election (yeah I know he won the popular vote by 500,000) in a year with no wars or foreign policy debacles, 3.8 % unemployment, 4% GDP growth year over year and a budget surplus of $200 billion dollars.
In a similar yet slightly less advantegous year, GHW Bush won by nearly 8 points over Michael Dukakis (5% unemployment, 4% GDP growth and a $150b deficit).
The period 1996-2000 was one of the strongest in post WW2 history and yet Gore lost. No recession, no war and you lose. 1984-1988 was almost as good and the incumbent party won 426 EVs.
Gore was trailing by a lot for most of the election, before he did clearly have the votes to win, but it just wasn't by enough of a margin to become President. Of course Bush would have easily won without his DWI being disclosed shortly before the election.