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The POSSIBLE WINNER problem asks, given an election where the voters' preferences over the candidates are specified only partially, whether a designated candidate can become a winner by suitably extending all the votes. Betzler and Dorn [1] proved a result that is only one step away from a full dichotomy of this problem for the important class of pure scoring rules in the case of unweighted votes and an unbounded number of candidates: POSSIBLE WINNER is NPcomplete for all pure scoring rules except plurality, veto, and the scoring rule with vector (2, 1, . . . , 1, 0), but is solvable in polynomial time for plurality and veto. We take the final step to a full dichotomy by showing that POSSIBLE WINNER is NP-complete also for the scoring rule with vector (2, 1, . . . , 1, 0).

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