For Democrats who want their party to meet the needs of working Americans — not just split the difference between Wall Street and everybody else — last weekend’s party convention in New York provides a ray of hope.

Except — bewilderment alert! — it wasn’t a Democratic Party convention. It was the convention of a third party, the avowedly social democratic Working Families Party. And by skillfully playing its hand, the WFP managed to compel New York’s nominally Democratic governor, Andrew Cuomo, to publicly promise to campaign for a Democratic state senate, rather than the Republican senate he had effectively supported until last Saturday.

Understanding the complexities of New York politics requires a short course in both the state’s electoral fusion laws and the ambitions of its governor. In New York, minor parties can choose to endorse major parties’ candidates, provided those candidates want the endorsement, or they can back candidates of their own. Since its founding in 1998, the WFP has almost invariably backed liberal Democrats, though in a very few instances, it has run its own candidates against more right-leaning Democrats.

The question before the WFP’s convention was whether it should mount such a challenge against Cuomo, who is seeking reelection. Though liberal on social issues — he pushed bills through the legislature establishing same-sex marriage and strengthening gun controls — Cuomo largely dismissed the rising clamor for policies that would raise wages and diminish the role of money in politics. Like a number of Republican governors, he opposed letting cities set their minimum wages higher than the state’s — a policy change that New York City Mayor Bill de Blasio requested. Cuomo said he was powerless to help enact the kind of campaign finance law that New York City adopted for its own elections, in which all contributions under $175 are matched 6-to-1 with public funds. Neither of these initiatives could get through the state’s senate, where five Democratic senators had aligned themselves with the Republicans to effectively transfer control to the GOP.

The five Democrats’ defection plainly suited Cuomo’s purposes, ensuring that legislation upsetting to New York’s business interests would never reach the governor’s desk. Those interests, particularly Wall Street, have been very good to Cuomo, helping him build a campaign treasury in excess of $30 million and holding the potential to help fund a presidential bid, should Hillary Clinton choose not to run in 2016. The composition of the Senate, Cuomo accordingly insisted, was none of his business: He wouldn’t back primary campaigns against the Democratic defectors.

Cuomo’s willingness to bottle up key Democratic proposals rankled many of the party’s rank-and-file. In the past month, polls showed Cuomo defeating a Republican in a two-way gubernatorial race this November by roughly 30 points. But when two polls added an unnamed Working Families Party candidate to the mix, Cuomo’s share dropped to 38 percent, while the WFP candidate drew 23 percent (and the Republican, 24 percent). If Cuomo wanted the kind of big victory that can propel a governor toward the White House, he had to persuade the WFP to nominate him.

Most of the unions that back the Working Families Party, sadly, wanted it to endorse Cuomo without extracting any concessions. Unions have been down so long that Cuomo looked like up to them. As the convention approached, however, party leaders recruited a compelling potential challenger — Zephyr Teachout, a Fordham law professor — and informed the governor that he would have to reverse field on a number of policies if he hoped to win the party’s backing.

So Cuomo reversed. He agreed to support raising the state minimum wage to $10.10 an hour and to permit cities to set their own wage standard 30 percent higher than that. He committed to passing the same public financing election law that New York City had enacted. Above all, he pledged to campaign against the defector Democratic senators unless they returned to the fold. (They soon may.) That sufficed to win him the WFP’s nomination.

Some WFP members accused party leaders of deal-making — as if all deals were created equal, as if there weren’t good deals and bad. What the WFP secured was a very good deal — and in so doing, provided a lesson for Democrats nationwide who are nervous about Clinton’s economic views. The lesson is that a primary challenge from Clinton’s left is likely the best way to ensure that a Clinton presidency doesn’t just split the difference between Wall Street and everybody else.

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