There are hundreds of Dem super-delegates that are currently expected to vote for Clinton, but could be convinced to switch to Sanders. According to RealClearPolitics (link below), currently Clinton has 469, Sanders 29, and 214 yet to be determined.
Will Sanders win 100 super-delegates? (Sanders wins 71 of remaining 214)
Will Sanders win 150 super-delegates? (Sanders wins 121 of 214, or flips some of Clinton's)
Will Sanders win 250 super-delegates? (mathematically requires flipping lots of Clinton's)