Siena Poll Shows Gendebien Leading Constantino in NY-21

Anthony Constantino holds a 71% implied probability of winning the NY-21 House race, down from 82% three days ago, after a Siena Research Institute survey released October 9 showed Democrat Blake Gendebien leading 46% to 42% among likely voters, with 8% undecided. It is the first public poll of this cycle to put the Democratic candidate ahead in NY-21.

Prediction markets have responded. That 11-point contraction across Kalshi (72%) and Polymarket (70%) reflects a market that had priced this seat as nearly safe and is now repricing risk in real time.

Live market odds

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NY-21 House winner?

Each outcome's chance, from what traders are paying right now on Kalshi, Polymarket US, Polymarket and Predict.fun.

Anthony Constantino (R)In this story

66%

PolymarketBest price1.49x67¢Predict.fun1.48x67.6¢Kalshi1.47x68¢

Blake Gendebien (D)

33%

KalshiBest price3.23x31¢Polymarket US2.94x34¢Polymarket2.86x35¢Predict.fun2.82x35.4¢

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Siena Poll Flips the Script on NY-21: Gendebien Leads in a Former "Solid R" District

The timing tells the story. On September 25, the Cook Political Report downgraded NY-21 from "Solid R" to "Likely R." That shift acknowledged structural vulnerability but still implied a comfortable Republican hold. Two weeks later, Siena's field work (September 30 to October 6) produced a result that went past "Likely R" territory entirely: a 4-point Democratic lead.

That sequence, from ratings downgrade to adverse polling, is exactly the kind of compounding signal that forces rapid repricing. A single poll in a low-attention House race would normally draw skepticism. But when the nonpartisan ratings outfit has already flagged the seat as weakening, a credible pollster confirming that weakness carries outsized weight. Siena is an A-rated pollster with a long track record in New York state races, and its likely-voter screen adds methodological credibility that a registered-voter survey would lack.

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Is NY-21 Actually a Competitive Race in the 2026 Midterms?

NY-21 spans most of upstate New York's northern tier, from the Adirondacks east to the Vermont border and west toward Watertown. The district is geographically vast, predominantly rural, and has leaned Republican in recent cycles. Constantino won 59.3% in the June 23 Republican primary over Assemblyman Robert Smullen, according to local reporting, consolidating the GOP side early.

But "lean Republican" and "safe Republican" are different claims, and the national environment matters. The party holding the White House historically loses House seats in midterm elections, and energy costs have emerged as a crosscutting issue in upstate New York. Axios reported on October 6 that energy prices are looming large in key House races, a dynamic that plays directly into rural districts where heating bills consume a larger share of household budgets.

Gendebien, a dairy farmer from Lisbon, brings a candidate profile suited to the district. He is not a parachute candidate from a downstate metro area. His agricultural background gives him cultural credibility in a region where farming and land use dominate local politics. On the money side, Constantino holds a fundraising advantage ($9.5 million raised, $3.0 million cash on hand versus Gendebien's $5.5 million raised and $2.6 million cash on hand), but the gap is not insurmountable, especially if national Democratic groups begin redirecting resources to a newly competitive seat.

The NRCC's calculus is worth watching. House GOP Whip Tom Emmer has publicly discussed limiting spending to districts with the "biggest return", which could mean NY-21 gets reinforced or, conversely, that resources flow elsewhere if internal polling confirms the race is tightening beyond easy rescue.

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Are There Polls for the NY-21 Constantino vs. Gendebien Race?

Three public polls have surfaced in this cycle, and they tell a story of erosion.

A J.L. Partners survey from August 17 showed Constantino ahead by 10 points, 50% to 40%. That double-digit lead was consistent with a "Solid R" rating and the market's earlier 82% pricing. A Public Policy Polling survey from September 10 narrowed the margin to 5 points, with Constantino at 48% and Gendebien at 43%. Then came the Siena poll on October 9: Gendebien 46%, Constantino 42%.

The trendline is unmistakable. Constantino's lead went from +10 to +5 to -4 across three polls spanning roughly seven weeks. Markets, which priced Constantino at 82% before the Siena release, have adjusted to 71%, a move that acknowledges the tightening but still assigns nearly three-in-four odds to the Republican.

The gap between the polling picture and the market price is the core tension. If you weight the Siena poll heavily, 71% for Constantino looks generous. A 4-point deficit among likely voters, with only 8% undecided and less than four weeks until Election Day, is a genuinely difficult position. But prediction markets are not poll aggregators. They discount for sample size, pollster lean, and the possibility that a single survey is an outlier. The earlier J.L. Partners and PPP numbers still anchor the market's prior, and one Siena poll, however credible, may not be enough to push Constantino below 65%.

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The Case Against Constantino: What Would Need to Be True for 71% to Be Wrong?

If the Siena poll is directionally correct rather than a statistical fluke, Constantino faces a convergence of problems that 71% may understate.

First, the undecided voters. Eight percent of likely voters remain uncommitted. In a midterm environment where the incumbent president's party typically bleeds support, late-breaking undecideds in competitive House races tend to split toward the challenger. If Gendebien captures even a slight majority of that 8%, his 4-point lead could widen to 6 or 7.

Second, Gendebien's $2.6 million cash on hand still buys meaningful contact in a media market as inexpensive as upstate New York. Television ad rates in the Watertown and Burlington, Vermont, DMAs are a fraction of what candidates pay in New York City or Long Island. Dollar for dollar, Gendebien's war chest stretches further here than almost anywhere else in the country.

Third, if the DCCC reclassifies NY-21 as a pickup opportunity following this poll, an influx of outside spending could overwhelm Constantino's existing financial advantage. National groups have shown willingness to flood late money into races where a single poll signals vulnerability.

For 71% to be correct, you need to believe the Siena poll overstates Gendebien's strength by at least 4 to 5 points, that the August and September surveys better capture the electorate's composition, and that Constantino's fundraising edge will translate into a late-breaking surge. That is a defensible position. But it requires dismissing a trendline of three consecutive polls moving in the same direction, from a 10-point Constantino lead to a 4-point deficit, as noise rather than signal.

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What Happens Next: Resolution and Key Dates

The NY-21 House race resolves on November 3, 2026, leaving 25 days for the market to price in additional polling, spending data, and any late-cycle developments. The next major inflection point will be whether a second pollster confirms the Siena finding. A corroborating survey from another A-rated firm would likely push Constantino's implied probability into the low 60s or below. Conversely, if an October poll from PPP or J.L. Partners shows Constantino back in front, the market could rebound toward 80%.

For now, the 2-point spread between Kalshi (72%) and Polymarket (70%) suggests both platforms are processing the same information. Track live prices and resolution details on the NY-21 House winner odds page.

The market's message is clear: Constantino remains the favorite, but "Solid R" is dead. This is a real race.