A MONG THE reasons why Donald Trump won the White House, America’s system of choosing presidential nominees is rarely discussed. Yet it was the Republican Party’s winner-take-most allocation of primary delegates that let him convert a series of narrow pluralities into a large lead. Next week, the Democrats’ primary season begins with the Iowa caucuses. In an echo of 2016, Bernie Sanders, a factional leftist, leads the polls in the first states to vote.

Could history repeat itself? To avoid such an outcome, the Democrats distribute delegates in proportion to votes. But this carries its own hazard. If no one wins a majority, delegates to the party’s convention choose the victor. That could leave the nominee without democratic legitimacy.

Both risks can be avoided using ranked-choice voting ( RCV ), in which voters rank as many candidates as they want from first place to last. If no one wins at least half of first-choice votes, the least-popular option is eliminated, and all ballots cast for them are reallocated to those voters’ second choices. The process repeats until someone wins an absolute majority.

Six states are set to use a partial form of RCV in their primaries. And in the general election, Maine will become the first state to cast electoral votes using RCV .

What would happen if the Democrats held a national RCV primary? YouGov, a pollster, recently asked 2,000 voters to rank the candidates. Its data show that Joe Biden, the national polling leader, would also win under RCV . But he would owe his victory as much to the stubbornness of Mr Sanders’s fans as to his own popularity. ■

Source: YouGov/The Economist