Strategic vote trading under complete information

We study two-party elections considering that: (a) prior to the voting stage voters are free to trade votes for money according to the rules of the Shapley-Shubik strategic market games; and (b) voters' preferences - both ordinal rankings and cardinal intensities - arepublic information. While under plurality rule no trade occurs, under a power-sharing system (voters' utilities are proportionally increasing in the vote share of their favorite party) full trade is always an equilibrium (two voters - the strongest supporter of each party - buy the votes of all others). Notably, this equilibrium implements proportional justice with respect to the two buyers: the ratio of the parties' vote shares is equal to the ratio of the preference intensities of the two most opposing voters.