Eric Maskin and Amartya Sen in NYT Sunday Review:

The Marquis de Condorcet, the great 18th-century political theorist and mathematician, proposed a system for electing candidates who truly command majority support. In this system, a voter has the opportunity torank candidates. For example, her ballot might rank John Kasich, Ted Cruz and Mr. Trump in that order, meaning that she likes Mr. Kasich best, but if he doesn’t win, she would go for Mr. Cruz. She could, alternatively, choose to vote just for Mr. Kasich, which would amount to ranking Mr. Trump and Mr. Cruz in a tie for second. The winner would then be the candidate who, according to the rankings, would defeat each opponent individually in a head-to-head matchup — a real majority winner. (For simplicity, we have described a winner-take-all case; Condorcet’s prescription would also be applicable in primaries where delegates are assigned proportionally.)