Hillary Clinton holds a 12 to 14 percentage point lead in surveys of New York Democratic primary voters ahead of tomorrow’s election, setting the stage for a decisive victory over senator Bernie Sanders.

But Sanders and his backers have at least one thing going for them: the performance of Zephyr Teachout, a law professor and progressive Democrat who mounted an intra-party challenge against New York governor Andrew Cuomo in 2014.

Written off as a gadfly (sound familiar?) most pollsters didn’t bother tracking her challenge. One private poll released by an organization backing Teachout the day before the election saw her garnering only 26% of the vote; political hands expected her to gain perhaps a quarter of the state’s voters in a three-way match-up.

But Teachout won 34% of the vote, a result that shocked political observers. It dented Cuomo’s presidential aspirations well before US Attorney Preet Bahrara’s corruption investigations put the final nail in their coffin.

Teachout made corruption her touchstone, highlighting Cuomo’s connections to New York’s legendary statehouse corruption and the broader ideological compromises of centrist wing of the Democratic party.

Of particular interest for Sanders: Teachout did better than Cuomo in upstate New York, where her firm stance against hydraulic fracturing, aka “fracking”, contrasted with the governor’s then-ambivalence. Sanders has sought to exploit the same contrast with Clinton by calling for a nationwide ban on the drilling technique, which can contaminate groundwater among other environmental issues.

Cuomo, having initially under-estimated his challenger, has learned from her: He signed a fracking ban just months after his re-election, then adopted and enacted Teachout’s goal of a $15 state minimum wage.

Teachout is now running for Congress in an upstate district where she won 11 of 19 precincts in 2014. Sanders, responding to criticism that he has not contributed enough of his fundraising prowess to the party, recently sent out an e-mail urging his backers to contribute to Teachout’s campaign.

When it comes to Sanders’ own effort, he faces a tougher opponent in Clinton, whose organization is no longer taking Sanders lightly. Clinton, whatever her flaws, remains more popular with the party’s base than Cuomo.

Teachout’s effort is evidence that the left can surprise in a New York Democratic primary, and with the example of Michigan’s polling miss still visible in the rear-view mirror, there’s still hope for the Sanders camp.

A small margin victory would not immediately change Sanders’ odds of winning the Democratic nomination this summer. It might, however, change the story around his candidacy, giving his message a bigger platform in the final weeks of the contest, and a bigger opportunity to influence the party going forward—just as Teachout did.