It is arguably the most important single question in US politics today: How can the United States halt its downward spiral into extremism, gridlock and cross-partisan hatred?

For many advocates, a critical piece of the answer is the electoral reform known as ranked-choice voting.

“It reduces the incentive to be divisive as a strategy,” says Anna Kellar, director of the League of Women Voters of Maine and a leader in the 2016 drive that got the reform adopted in that state.

In fact, it turns the incentives around, says Kellar: Because a ranked-choice system automatically transfers people’s votes to their second, third or later choice of candidates if their first choice loses, candidates are forced to treat everyone as a potential supporter.

The result, hopefully, will be campaigns that reward bridge-building and broad appeal instead of attack ads, culture wars and exciting the base and in the process, de-inflame our politics.

That hope is one big reason why US foundations, philanthropists and individual donors have been pouring money into ranked-choice reform efforts for the better part of a decade. And it’s why ranked-choice voting, also known as instant-runoff voting, has already been adopted in dozens of US cities and states.

These early adopters range in political affiliation from the 23 cities in ruby-red Utah that will start using ranked-choice voting in November, to the independent-friendly states of Maine and Alaska, to Democratic bastions such as San Francisco and Berkeley and now New York City, which became by far the most populous member of the group when it used ranked-choice voting for the first time in its June 22 mayoral primary.

In the past two decades, ranked-choice voting has spread from a single outpost in Cambridge, Massachusetts, to dozens of US cities and states – most of them within the past five years.

Proponents have high hopes that this cross-partisan momentum will continue. “I think we’re going to see every jurisdiction using ranked-choice voting in 10 years,” declares Rob Richie, CEO of the ranked-choice research and advocacy organisation FairVote.

Yet that is hardly a foregone conclusion. Ranked-choice voting still feels new and strange to most Americans, and poses a host of questions. How does it work, for starters? Is it too complicated for voters to understand? Can it actually deliver on its promises? And does it have any hope of surviving in the current political climate? 

Ranked-choice voting is neither new nor untried. The idea itself dates back at least to the 1850s, and it’s been used for national elections in Australia and Ireland for a century now. Its prime motivation – leaving aside, for the moment, the promise of calming political waters – is to solve a specific set of problems that exist with “plurality” voting: the familiar system that has long been the norm in the United States, the United Kingdom and many other countries.

Plurality voting does have the virtue of simplicity: Whoever gets the most votes wins. But in close races it is vulnerable to the kind of third-party spoiler effect made infamous in the 2000 US presidential election: The tiny fraction of votes that went to activist and Green Party candidate Ralph Nader in Florida almost certainly cost Democrat Al Gore the state and the presidency.

Many jurisdictions try to get around this issue by holding a runoff election between the top two vote-getters. But runoffs tend to be time-consuming, expensive and – because turnout is usually abysmal – decided by a small fraction of the total electorate.

Even worse, plurality voting can produce winners that most voters don’t want: candidates who squeak into office only because two or more rivals split the opposition. Easily the most consequential recent example was the 2016 US presidential contest, when Donald Trump prevailed in the crowded Republican primaries with just 45 per cent of his party’s vote.

Another was the 2010 election of Maine Governor Paul LePage, a divisive, confrontational figure who won a four-way race with 38 per cent of the vote. And had the September 14 recall effort against California Governor Gavin Newsom not been defeated, he would have been replaced by Republican Larry Elder – whose polling average on election eve was less than 30 percent.

Reformers often argue that examples like these aren’t anomalies — that the plurality system has increasingly turned negative campaigning and extremism into an effective campaign strategy. Get enough of your supporters excited, after all, and it doesn’t matter how many other voters you alienate: A non-majority win is still a win.

But the system can also undermine even the best winner’s legitimacy, says Jason Grenn, director of the ranked-choice advocacy organisation Alaskans for Better Elections. When his state adopted ranked-choice voting in 2020, he says, Alaska hadn’t elected a US Senator with more than 50 percent of the vote since 2002. “It’s a tough message for a winner to say, ‘OK, I’m going to DC with 40 percent approval but 60 percent of my district didn’t support me,’” he says.

Ranked-choice voting is designed to solve all these problems by producing officeholders who have majority support. Here’s how it works:

First, voters are asked to rank the candidates by preference on election day, instead of choosing just one. (And no, you can’t leave middle rankings blank and mark your least-favoured choice as last.) If the tally then shows that someone got more than half of the first-choice votes, as Republican Susan Collins did in Maine’s ranked-choice 2020 election for the US Senate, they win outright and everything proceeds as before.

But if no candidate gets more than half of the first-choice votes, the counting goes into instant-runoff mode: The candidate with the lowest total is eliminated – think Nader (and others) in the Florida 2000 example – and their votes are reallocated to their supporters’ second choices.

This elimination process then repeats through as many rounds as needed, until one candidate passes 50 percent. New York’s crowded Democratic primary turned out to be a classic example: Candidate Eric Adams went from 30.7 per cent of the vote in the first round to 50.4 per cent and victory in the eighth.

• A Knowable Magazine report