Lose the Jewish vote . . . a reliably Democrat constituency . . . and it's pretty much over. The money they donate will follow them away.
Like it or not, though, he will still have upwards of 95% of the Black vote, purely on racial affiliation, without even getting to the 'free ponies' issue. The only question with that voting block will be whether or not he has screwed things up so royally that they just find something else to do that day instead of dutifully trooping to the polls to rubberstamp the "Man of (The Right) Color."