New Yorkers weighing November’s referendum on adopting ranked-choice voting can look back 80 years to when city residents adopted a different electoral reform, proportional representation, and see how it affected election results. The measure reduced the power of the Democratic Party’s machine at the time, and it’s likely that ranked-choice voting, also known as instant-runoff voting, would have the same effect.

In the wake of a scandal involving widespread collusion between the NYPD and elected judges, with judicial decisions being fixed, Judge Samuel Seabury was appointed in 1930 to investigate corruption in city government, according to a 2017 report by FairVote. The investigation uncovered widespread corruption under Tammany Hall, the political machine at the time. Seabury concluded that the lack of competition in the city’s elections was a significant factor in how Tammany had become a machine, and recommended switching to a multimember district, single transferable vote system, which combines ranked-choice voting with large, multimember constituencies to achieve nearly proportional representation in a legislature.

The investigations led to the 1932 resignation of Democratic Mayor Jimmy Walker and the victory of reformer Fiorello La Guardia on the Republican and City Fusion ticket. La Guardia, a supporter of proportional representation, empaneled a charter revision commission in 1935 that recommended adopting that system. Virtually everyone except Tammany was in support. Republicans, good-government groups like Citizens Union and The New York Times all endorsed the measure. In the November 1936 election, New York City voted, by a nearly 2-to-1 margin, to abolish the Board of Aldermen and replace it with the City Council, which would use proportional representation.

Instead of running within single-member constituencies, the seats were at-large for each borough, and voters chose multiple candidates. The number of seats allocated to each borough was determined by the number of valid votes cast within the borough. For every 75,000 votes cast in a borough, a seat was allocated, causing the body to have a number of members that fluctuated between 17 in 1943 and 26 in 1937 and 1941, according to Drexel University professor Jack Santucci. Any candidate who won more than 75,000 votes was elected to the council. For candidates that did not reach the 75,000-vote threshold, a series of calculations would determine voters’ ranked preferences to fill the remaining seats.

The result was immediate: In the 1937 City Council elections, the Democrats’ supermajority collapsed. In 1935, Democrats won 66% of the votes in Board of Aldermen races, capturing 62 out of the body’s 65 seats. Republicans received 26% of the citywide vote but only won three seats. In 1937, Democrats won only half of the seats.

The beneficiaries were not solely Republicans: The union-backed American Labor Party, which provided a New Deal-supporting home for workers disillusioned with Tammany, won a fifth of the council seats, proportional to its share of the citywide vote. Also joining the council were independents, anti-Tammany Insurgent Democrats, and Fusion candidates. Together with a new rule requiring a supermajority to send items to the Board of Estimate, the new parties formed a solid bloc to check the power of Tammany. “With the way that the rules were set up, you actually needed a two-thirds supermajority to do anything of consequence,” said Santucci, whose research focuses on the history of proportional representation in America.

The new council much more faithfully represented the ideological diversity of the city, with parties winning approximately the same proportion of seats as they had total citywide votes. And unlike in the aldermanic days, when party candidates were hand-picked by local political bosses, anyone with 2,000 petition signatures could get on the boroughwide ballot under any party line they wanted, breaking Tammany’s grip on the City Council, according to FairVote.

“One-party monopolies are more in line with the dictatorships of Europe than with American democracy,” said George Hallett of Citizens Union, a major supporter of proportional representation, in a 1947 debate on WNYC with onetime state Sen. Abraham Kaplan on whether to abolish it. “We like to see an opposition to keep the majority on its toes, and to bring out the issues of all problems as they come up.”

The new council also demonstrated far greater independence from the established organs of political power than under the Board of Aldermen. The Board of Aldermen typically were a do-nothing group that passed little of substance, deferring real power to the Board of Estimate, which was responsible for land use and budgetary policy, according to George McCaffrey’s 1939 paper “Municipal Affairs: Proportional Representation in New York City.”

Under proportional representation, the City Council was highly productive. In particular, it passed numerous laws related to housing: It passed the Vladeck Housing Law – creating the city’s first subsidized housing program, albeit via “slum clearance” and with income requirements that excluded low-income residents, since public housing was initially set up for middle-class white residents – as well as a rent control bill in 1947 to counteract a weakening of rent regulations by Congress, according to Frederick Shaw in his 1954 book “The History of the New York City Legislature.”

Seabury referred to the 1946-49 session, which saw the highest productivity of the proportional representation sessions under a unified Democratic Board of Estimate and City Council (with the addition of minor-party allies), “the best legislature we have had so far.”

The new City Council, with its diverse partisan makeup, led to increased productivity and increased drama, and fostered greater civic engagement in municipal affairs among the city’s populace. Shaw noted that City Council meetings were broadcast over the radio and reached audiences of up to 750,000 people. And sleepy hearings on boring, arcane topics made way for vigorous debate on important issues of the day. “In place of countless permits for street stands and designation of individual play streets, (the City Council) became interested in citywide issues, such as housing, regulation of consumer commodities and civil service reform,” Shaw wrote. “The general police power was employed more vigorously, and greater interest was displayed in reforming the city government.”

The system’s opponents, mainly but not exclusively from Tammany, drew up several arguments in an attempt to restore the old order: that proportional representation would cause gridlock by introducing too many competing factions, and that the system was confusing to voters.

“Proportional representation is un-American, undemocratic, cumbersome, expensive and foreign to our American two-party system and should be abolished,” Kaplan said in the WNYC debate. Kaplan made not only process arguments against proportional representation but also inflammatory, prejudiced arguments as well. “Proportional representation invites racial groups, language groups, radical groups to intensify their differences by bringing them into political action,” he said. “The wise majority system of election invites them to forget these distracting prejudices while joining in the task of selecting capable men to look after the interest which they have in common.”

Opponents made several abortive efforts to restore the old system. At the 1938 state constitutional convention, delegates introduced an amendment to ban proportional representation systems in municipal elections statewide. (Yonkers also had a version of the system at the time, as did many other cities in the nation, including Cleveland and Cincinnati.) The state roundly rejected the amendment at the ballot box, by a margin of 2-to-1, according to the 1948 paper “The Repeal of P.R. In New York City – Ten Years In Retrospect” by Brooklyn College’s Belle Zeller and the University of Washington’s Hugh Bone. In 1940, a referendum on a city charter amendment to abolish proportional representation was rejected by New York City voters as well, though by a smaller margin of 58% to 42%, also according to Zeller and Bone.

But in 1947, opponents were successful in abolishing the system. At the time, two Communist Party members were serving on the City Council: Peter Cacchione of Brooklyn (first elected in 1941) and Benjamin Davis of Harlem (first elected in 1943). Cacchione and Davis, along with the Bronx’s Mike Quill, who was concurrently serving as a council member and as the president of the Transport Workers Union at the time, formed a left-wing bloc on the City Council.

They were easy targets for anti-Communist fervor, and soon Republicans and the press joined with Democrats to support abolishing proportional representation, which had enabled the election of Communist Party members. “People made a really big deal about the communists in order to get voters to support repeal, but they had other motives,” Santucci said.

In the WNYC debate, Hallett accused the opposition’s scare tactics as a veil for a more simple desire to return to dominance in elected government. “The chief real reason for the attack, I think, is clear,” Hallett said. “And that is that the Democratic leaders begrudge the large share of the council they have regularly lost to minority parties and independents under (proportional representation).”

New York City voters reversed their previous position in a 1947 referendum, voting by a nearly 3-to-1 margin in favor of returning to single-member council districts. In the 1949 election, the first after the end of proportional representation, Democrats won 24 out of 25 seats on the council with just 53% of votes citywide.

Nonetheless, proportional representation had a significant effect on the city’s political institutions. Tammany’s resurgence was short-lived, and its grip on the city’s Democratic Party would vanish in the 1960s. The City Council did not return to the do-nothing, toothless days of the Board of Aldermen, but instead retained its role as a more independent legislative body, conducting oversight hearings and passing substantive legislation.

But the New York City Council today is comprised of 48 Democrats and three Republicans, despite Democrats having won about 75% of the vote citywide. Third parties are historically weak, and despite having weathered significant defeats in recent years, the city’s elections remain heavily influenced by party machinery: endorsements by Democratic clubs are highly sought after by politicians, incumbents often resign after petition deadlines in order to place a hand-picked successor on the ballot and county party organizations have historically played a heavy role in the selection of the City Council speaker.

It’s unclear how much ranked-choice voting could alter New York City politics, especially when its confined to primaries and special elections. Much of the support within political circles comes down to the cost savings from not having costly runoff elections, but there is ample reason to believe that the reform could make the City Council – a body where a failed floor vote is exceedingly rare – more ideologically diverse, potentially benefiting those in the ideological middle and on the fringes. “Ranked-choice voting has the potential to moderate candidates’ positions on policies as they appeal to a broader spectrum of primary voters,” Alex Camarda, senior policy adviser at Reinvent Albany, wrote in an email. “At the same time, it allows nontraditional candidates to compete without being dismissed as spoilers.”

Correction: This piece originally contained an inaccurate characterization of how New York City Council seats were allocated to each borough under proportional representation.