Candidates, their staffs and consultants are all in the business of optimism. Give us money, and we can win. Volunteer, and we can win. Vote, and we can win. And they're not wrong to be optimistic. Individual Democratic candidates across the South — along with those in tight contests in Alaska, Colorado and Iowa — might each pull out a victory. (I don't know where to begin with this Kansas race.) Consequently, they don't want the president tossing up the chess board in hopes that the pieces land more favorably — not when they're just one debate triumph, or one opponent's gaffe, away from eking out a victory.