When voters head to the polls Tuesday to pick St. Louis’s next mayor, they’ll be faced with four names on the ballot. But unlike in most other elections, they won’t have to choose just one candidate to vote for. Instead, St. Louisans will experiment with a new form of voting that allows them to vote for as many candidates as they like.

In November, St. Louis voters passed Proposition D, which switched the city’s municipal elections to a nonpartisan “approval voting” system. The way it works is that voters can vote for as many candidates as they think would make a good mayor (or whatever office is up for election) and the two candidates with the most votes advance to a head-to-head general election. (In other variants of approval voting, the person with the most votes is simply named the winner after one round of voting.)

Like its better-known cousin, ranked-choice voting, approval voting is a popular proposal among election reformers looking to fix the flaws of our first-past-the-post electoral system (i.e., the election system you’re probably most used to: voters pick only one candidate, and the candidate with the most votes wins, regardless of whether they get a majority). By allowing people to vote for multiple candidates, approval voting aims to remove the often zero-sum game of our politics, no longer forcing people to choose between a candidate they love who has little chance of winning and a more viable candidate about whom they are less enthusiastic. For this reason, proponents argue that approval voting gives a fairer shot to third parties. It also theoretically eliminates the problem of vote-splitting. For instance, St. Louis is a plurality-Black city, but it has had a white mayor for the last 20 years in part because Black candidates have split the vote in the city’s predominantly Black north side. But under approval voting, Black voters will be able to vote for as many Black (and non-Black) candidates as they want.

Approval voting’s boosters also prefer it to ranked-choice voting because it’s simpler. Election officials can use the same ballots and machines they currently do, whereas ranked-choice ballots need to be redesigned to accommodate voters’ second, third, fourth, etc. choices. Ranked-choice voting can also lead to voter confusion and may lower turnout (although this is disputed), while approval voting actually produces fewer spoiled ballots — because a common reason ballots are currently disqualified is that voters vote for too many candidates. Approval voting also spits out results a lot faster than ranked-choice ballots, which can take days to tabulate.

Unlike ranked-choice voting, which is used by more than two dozen municipalities and now two states as well (Alaska and Maine), approval voting is just starting to catch on in American elections. The first jurisdiction to employ approval voting as its default voting method was Fargo, North Dakota, in its June 2020 municipal elections. Tomorrow, St. Louis becomes only the second member of the club, and also the one with the biggest population.

So far at least, the transition seems to be going smoothly. “For us as election officials, it really didn’t make any difference,” Cass County Finance Director Mike Montplaisir, who runs Fargo’s elections, told FiveThirtyEight. “We’re still counting the number of votes each candidate gets; that’s not any different. It’s just a change in the wording on the ballot and in the programming” of the voting machines. And Rosetta Okohson-Reb, the campaign manager for St. Louis Treasurer Tishaura Jones (one of the front-runners for mayor), said it hasn’t changed her campaign’s strategy very much — apart from doing a bit more voter education than normal. “We’ve been fielding a lot of questions from voters,” she acknowledged.

At the same time, though, approval voting hasn’t quite lived up to its supporters’ lofty promises either. In the St. Louis mayoral election, it’s not going to benefit third-party candidates, for instance; although the race is nominally nonpartisan, three candidates identify as Democrats and the fourth is a Republican. (Getting rid of the signature requirement for making the ballot would probably be a bigger deal to third parties.) Nor does it look like approval voting “fights big money in politics,” as supporters of Proposition D argued it would. The four candidates and their political action committees have raised more than $1.4 million, and the candidates who are leading in fundraising were also leading in a recent poll of the race.

Well-funded candidates furthest ahead in St. Louis

Fundraising totals (through Feb. 18) and vote share in a Remington Research/Missouri Scout poll (conducted Feb. 3-4) for the four candidates for St. Louis mayor

Candidate	Party ID	Money Raised	Vote Share in Poll
Lewis Reed	D	$531,000	59%
Tishaura Jones	D	456,000	51
Cara Spencer	D	433,000	40
Andrew Jones	R	19,400	19

And while there’s a good chance that St. Louis will finally get a Black mayor this year, that’s due more to the runoff provision than approval voting itself. With just one white candidate, Alderwoman Cara Spencer, in the race, the general election will either feature two Black candidates (thus guaranteeing the election of a Black mayor) or one Black candidate and one white candidate (thus avoiding vote-splitting by race).

What’s more, approval voting may not change voters’ behavior in practice; even though they have the option to vote for multiple candidates, they might just do what they’ve always done and vote for only one — either by choice or because they aren’t aware of the new rules. Fargo provides some grist for this theory: In its inaugural approval-voting election last June, 18,805 voters cast 42,855 total votes for city commissioner, for an average of 2.28 votes per person. But two seats on the commission were up for grabs in that election, meaning that even in the pre-approval-voting days, voters would have been allowed to vote for up to two candidates. So not too many people actually took full advantage of approval voting, and accordingly, Montplaisir told us he didn’t think it made any difference in who won.

In fact, it may actually be in voters’ best interests not to vote for multiple candidates. Although approval voting eliminates certain kinds of tactical voting and zero-sum thinking, it encourages others. For example, in the Fargo City Commission race, Montplaisir said that he himself “voted for only one candidate — the candidate I wanted to win — because voting for anyone else is like taking a vote away from [my first choice].” And, he added, “if there were a candidate I didn’t want to win, I’d vote for all the candidates except that one. You can game the system.”

We obviously don’t know the end of the story in St. Louis yet, but we do know that approval voting is injecting extra uncertainty into what was already an intriguing and unpredictable mayor’s race. Will Spencer snag one of the two general-election slots because voters continue to vote for just one candidate and voting remains polarized along racial lines? Will the city’s few Republicans use their extra votes to boost Board of Aldermen President Lewis Reed over the more progressive Tishaura Jones? Will Black voters use their clout to power both Reed and Jones into the general?

These are all important questions for the next four years of governance in St. Louis, but tomorrow’s broader legacy will be the success or failure of approval voting in its highest-stakes test yet. “I’m curious to see how engaged voters are, if it increases turnout here in the city,” Okohson-Reb mused. “I don’t know what people are going to do, and I’m very much looking forward to [seeing].”