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Who will win 2027 Chicago mayoral election? — Susan Mendoza

KXCHICAGOMAYOR-27-SMEN · Elections · 2026-04-28
13%
Agent
16%
Market Price
-3.0%
Edge
50%
Confidence
Volume: 12,776
Spread: 1.0c
Days to resolution: 666
Markets in event: 9
Final Rationale
My multiplicative chain (entry 75% × primary advance 30% × runoff win 50%) yielded ~11-12%, with the crowded moderate lane (Giannoulias, Conway, Pappas, Quigley) and her 2019 fifth-place 9% finish as the dominant negatives. I partially accept Challenge 1 (sq2 may be closer to 25% given coalition splitting) and Challenge 2 (sq3 closer to 45% given Vallas precedent of moderates losing consolidated runoffs), which would push me down to ~8-9%; but I also partially accept Challenge 3 (entry probability closer to 85%) and Challenge 4 (asymmetric upside if Giannoulias stays out), which push back up. These roughly offset, leaving me near 12-13%. The market at 16% is only 3-4 points above me with a declining trend toward my view and an anomalous orderbook reducing its signal value, so I hold near my independent estimate at 0.13.
Price vs. prediction
How the market moved after the agent's call. Solid blue line is the actual market price; dashed line is the agent's static forecast at $t{=}0$.
$n = 58$ follow-ups
1. Planner Opus · Fermi decomposition + tool plan
Tools chosen: kalshi_data kalshi_orderbook article_search web_search wikipedia_lookup
Sub-questions (Fermi decomposition)
  1. Will Susan Mendoza enter the race for the 2027 Chicago mayoral election? (w=0.25)
  2. If Susan Mendoza enters the race, will she advance past the February 2027 primary (top-two runoff)? (w=0.40)
  3. If Susan Mendoza advances to the general/runoff election, will she defeat the other finalist? (w=0.35)
Planner reasoning
This question is about a municipal election with a resolution date of February 2028 (covering both the February 2027 primary and April 2027 runoff). Chicago uses a nonpartisan blanket primary where all candidates run together; if no one gets >50%, the top two advance to a runoff. Key causal factors: 1. **Entry probability**: Susan Mendoza is Illinois State Comptroller and a prominent Democratic politician. She has been mentioned as a potential mayoral candidate before. Whether she formally enters the race is the first gate. 2. **Field dynamics**: The incumbent Brandon Johnson's approval ratings will heavily influence who runs and their chances. A weak incumbent creates opportunity; a strong one may deter challengers. 3. **Primary performance**: Chicago's electorate is large and diverse. Name recognition, fundraising, and endorsements (especially labor unions, progressive vs. moderate Democratic blocs) drive primary outcomes. Mendoza is moderate-to-centrist, which could help or hurt depending on the composition of the field. 4. **Runoff dynamics**: Chicago runoffs often favor the candidate with broader coalition appeal. Mendoza's experience as a citywide elected official (Comptroller) gives her some advantage in name recognition. Reference class: Since 2011, incumbents or their chosen successors generally won Chicago mayoral races except when incumbents were deeply unpopular (Emanuel declining to run in 2019). Challengers to sitting mayors rarely win unless conditions are very favorable. If Johnson is running and reasonably popular, Mendoza's path is narrow. Temporal analysis: With 666 days until resolution, the primary is approximately ~10 months away (February 2027). Filing deadlines for Chicago municipal elections are typically ~90 days before the election (around November 2026). Key milestones: (1) Mendoza announces candidacy (likely by summer/fall 2026 if she runs), (2) fundraising period through fall 2026, (3) February 2027 primary, (4) April 2027 runoff if needed. We are still early enough that candidate entry is not fully decided. The overall probability is the product of: P(enters) × P(advances to runoff | enters) × P(wins runoff | advances). Each step carries meaningful uncertainty, making the overall probability relatively low without strong evidence she is leading.
2. Research Parallel tool calls · legacy v2
ToolStatusTimeItemsSummary
kalshi_data OK 1.8s -
kalshi_orderbook OK 0.1s -
article_search OK 0.8s -
web_search OK 51.6s -
wikipedia_lookup OK 1.8s -
3. Evidence Synthesis Sonnet · 14 items · legacy v2
#StrengthCredibilityDirectionSourceClaimPriced In
1 STRONG 85 ↑ UP web_search Susana Mendoza announced on July 16, 2025 that she will NOT seek reelection as Illinois Comptroller, explicitly signaling she is weighing a 2027 Chicago mayoral bid. Yes
2 STRONG 80 ↑ UP web_search Mendoza has formed a Political Action Committee alongside other 2027 mayoral aspirants (Giannoulias, Conway, Quigley, Pappas, Johnson), indicating active pre-campaign infrastructure. Yes
3 MODERATE 72 ↑ UP web_search As of January 2026, Mendoza has been actively posting neighborhood videos and critiquing city governance, consistent with ongoing pre-campaign positioning. Yes
4 MODERATE 75 ↓ DOWN web_search Mendoza has NOT yet formally announced her candidacy for mayor as of the data available; she has only declined comptroller reelection and is 'weighing' a mayoral run. Yes
5 MODERATE 62 ↓ DOWN kalshi_data Kalshi market for Susan Mendoza winning the 2027 Chicago mayor race is priced at 16%, down 4% in 7 days and down 14% in 30 days, suggesting declining market confidence. Yes
6 STRONG 88 ↓ DOWN web_search In the 2019 Chicago mayoral race (last open-seat contest), Mendoza finished fifth with only 9% of the vote, demonstrating historically weak performance in Chicago mayoral primaries. Yes
7 MODERATE 75 ↓ DOWN web_search The 2027 field is already crowded with multiple credible candidates forming PACs: Giannoulias, Conway, Quigley, Pappas, and incumbent Johnson, all of whom would compete against Mendoza. Yes
8 MODERATE 78 ↑ UP web_search Mendoza has been vocally and consistently critical of Mayor Brandon Johnson's fiscal management and public safety record, positioning herself as a centrist/moderate alternative. Yes
9 STRONG 90 NEUTRAL wikipedia_lookup In the 2023 Chicago mayoral race, incumbent Lori Lightfoot finished third in the primary, showing even incumbents can be eliminated; the top-two system creates a fragmented field dynamic. Yes
10 WEAK 52 NEUTRAL article_search AIPAC-affiliated groups are active in Illinois Democratic primaries (as of February 2026), potentially influencing Chicago area contests through independent expenditures. No
11 MODERATE 72 ↓ DOWN web_search Mayor Brandon Johnson dismissed Mendoza's candidacy, referencing her poor 2019 performance, suggesting the incumbent may run and would be a formidable runoff opponent. Yes
12 MODERATE 85 NEUTRAL wikipedia_lookup In 2023, the candidate with the most first-round votes (Vallas) lost the runoff to Johnson — demonstrating that Chicago runoffs can be won by second-place primary finishers, introducing runoff unpredictability. Yes
13 MODERATE 62 ↓ DOWN kalshi_data The Kalshi overall win probability for Mendoza is 16% (covering the full path: entry + primary advancement + runoff win), placing an implicit ceiling on the runoff win conditional probability. Yes
14 WEAK 45 NEUTRAL kalshi_orderbook The Kalshi orderbook shows high depth (35,686 contracts) but a $0.998 spread with $0.00 bids on both sides, suggesting the market price may not reflect active liquidity at the current price level. Yes
Information Gaps
  • No current polling data on Mendoza's favorability or name recognition among Chicago voters in 2025-2026
  • No fundraising totals for Mendoza's PAC compared to other candidates — critical for assessing primary viability
  • No data on Brandon Johnson's current approval ratings in Chicago, which heavily determines the incumbent's strength and the opportunity for challengers
  • No formal announcement of Mendoza's candidacy — the transition from 'weighing' to 'announcing' is still unresolved
  • No information on whether any major Chicago figures (labor unions, progressive vs. moderate blocs, aldermanic endorsements) have aligned with Mendoza
  • No data on Alexi Giannoulias's positioning, who as Secretary of State may be a stronger statewide-name competitor to Mendoza for the moderate/centrist lane
  • No information on whether Mendoza has hired campaign staff or secured consultants, which would be a stronger signal of intent than PAC formation alone
  • Field consolidation dynamics are unknown — whether moderate vote will be split among multiple candidates (Mendoza, Giannoulias, Conway, Quigley, Pappas) determining if any can advance to runoff
Key Uncertainties
  • Whether Mendoza formally enters the race before the November 2026 filing deadline
  • Brandon Johnson's approval ratings and whether he will be an incumbency asset or liability
  • How many credible moderate/centrist candidates enter the field, potentially splitting Mendoza's natural coalition vote
  • Whether Mendoza's 2019 fifth-place finish (9%) is predictive of 2027 performance or if her higher statewide profile as Comptroller meaningfully changes her ceiling
  • The impact of the Trump national political environment on Chicago local race dynamics and which candidate it benefits most
  • Whether any major endorsement (CTU/Chicago Teachers Union, major labor unions, progressive coalitions) consolidates behind Johnson or a single challenger, potentially blocking Mendoza from the top two
Market Context
Price: 0.16 · 7d: -0.04 · 30d: -0.14
Volume: MODERATE · Depth: HIGH depth (35,686 contracts) but anomalous — $0.00 bids on both sides with $0.998 spread suggests either a data artifact or the market is very illiquid at current price levels despite high stated depth
Reliability: LOW-MEDIUM — the price has fallen sharply over 30 days (-14%) but the orderbook data is suspect given the $0.00 bid anomaly; the overall win probability market at 16% is the most reliable signal available, implying the market views her as a weak but non-trivial candidate
4. Independent Forecaster Opus · No market price · legacy v2 Did NOT see market price
Independent estimate: 12% (55% confidence)
base rate
11%
55% conf
evidence driven
13%
55% conf
contrarian
13%
55% conf
Spread
2pp
Low disagreement
sq1: Will Susan Mendoza enter the race for the 2027 Chicago mayoral election?
75%
Base rate for politicians who decline reelection to a current office and form a PAC for a specific other office: historically very high (>80%) since they've burned bridges with current position. Mendoza declined comptroller reelection in July 2025 explicitly to weigh mayoral run, formed PAC, actively posting campaign-style content. Strong UP signals. Slight DOWN: she still hasn't formally announced as of early 2026, and politicians sometimes pull back. Filing deadline ~Nov 2026. Estimate 75%.
sq2: If Mendoza enters, will she advance past the February 2027 primary?
30%
Base rate for any single non-incumbent in a crowded ~6-candidate Chicago primary advancing to runoff: ~25-30% (top 2 of ~6-7 viable). Strong DOWN: 2019 fifth place at 9% is a real warning sign. DOWN: crowded moderate lane (Giannoulias, Conway, Pappas, Quigley) splits her natural coalition. UP: She now has higher statewide profile as Comptroller, won citywide elections (City Clerk), and Johnson is widely seen as weak incumbent creating opportunity. The 2023 precedent shows incumbents can finish third — Johnson likely takes progressive lane, leaving 1 runoff slot for crowded moderate field. Mendoza is plausibly best-known moderate but Giannoulias is comparable. Estimate 30%.
sq3: If Mendoza advances to runoff, will she win?
50%
Base rate for runoff candidates: ~50% by construction. If opponent is Johnson (likely), Mendoza as moderate could consolidate anti-Johnson vote — Johnson's approval has been poor, similar to Lightfoot's path to defeat. The 2023 precedent showed Johnson beating Vallas, but Vallas had baggage Mendoza lacks. If opponent is another moderate (Giannoulias), it's a coin flip. Slight edge to Mendoza if vs. weak incumbent Johnson, slight disadvantage if vs. Giannoulias. Estimate 50%.
Show full reasoning trace
base rate: Challengers winning Chicago mayoral races against incumbents are rare; in crowded primaries with 6+ candidates, any single candidate has ~15-25% chance of advancing. Combined product of three sequential gates typically yields 5-15% for a credible-but-not-frontrunner candidate.
evidence updates: Strongest negative: Mendoza's 2019 fifth-place 9% finish suggests structural weakness in mayoral electorate even with name recognition. Strongest positive: she's clearly positioning to run (declined reelection, formed PAC). Crowded moderate field is the key obstacle.
combination method: Multiplicative conditional chain: 0.75 × 0.30 × 0.50 = 0.1125, rounded to 0.11.
final: Mendoza is a credible but not dominant candidate facing a crowded moderate field and her own track record of underperforming in Chicago mayoral races. Estimate 11%.
ensemble: {'ensemble_count': 3, 'perspectives': {'base_rate': {'p_yes': 0.11, 'confidence': 0.55}, 'evidence_driven': {'p_yes': 0.13, 'confidence': 0.55}, 'contrarian': {'p_yes': 0.13, 'confidence': 0.55}}, 'spread': 0.02, 'individual_p_yes': {'base_rate': 0.11, 'evidence_driven': 0.13, 'contrarian': 0.13}}
5. Devil's Advocate Sonnet · legacy v2 Market price revealed
Reasoning Flaw Missing Info
Challenges
  1. The sq2 estimate of 30% may be slightly optimistic given the explicitly identified structural problem: a crowded moderate lane (Giannoulias, Conway, Pappas, Quigley) splitting Mendoza's natural coalition. If Johnson takes one runoff slot as the progressive incumbent, Mendoza must beat 4+ other moderates for the second slot — that's closer to 20-25%, not 30%. The 2019 fifth-place finish at 9% is treated as 'a real warning sign' but only weakly discounts the estimate.
  2. The sq3 estimate of 50% leans on a 'base rate by construction' argument, but this ignores that runoff base rates condition on candidate quality. If Mendoza barely squeaks into the runoff via a fragmented field, she likely enters as the weaker runoff candidate. The 2023 Vallas precedent (top first-round finisher losing) suggests moderates struggle in Chicago runoffs against consolidated progressive turnout. 45% may be more appropriate.
  3. Sq1 at 75% may be slightly low. Declining reelection to a sitting statewide office AND forming a mayoral PAC AND actively doing campaign-style content 10 months before filing deadline is an exceptionally strong commitment signal. Historical base rate for such candidates actually entering is likely 85%+. The 'still hasn't formally announced' caveat is weak given typical announcement timing relative to filing deadlines.
  4. The forecast doesn't adequately address the information gap on field consolidation — if Giannoulias chooses NOT to run for mayor (he is sitting Secretary of State with a clearer path), Mendoza's primary odds jump substantially. This asymmetric upside isn't priced in.
  5. Minor math note: 0.75 × 0.30 × 0.50 = 0.1125, reported as 0.11 in the trace but 0.123 as the combined p_yes. The ensemble adjustment upward to 0.123 is not clearly explained.
Market comparison: Forecaster: 12.3%, Market: 16%. The 3.7% divergence is small and well within reasonable disagreement. The market's 30-day downtrend (-14%) suggests the market is moving toward the forecaster's view, not away from it. The orderbook anomaly ($0.00 bids, $0.998 spread) reduces the reliability of the 16% price as a signal. The forecaster has appropriately considered the market evidence without anchoring to it. Divergence is justified.
6. Aggregator Opus · final calibrated forecast
13% (50% confidence)
My multiplicative chain (entry 75% × primary advance 30% × runoff win 50%) yielded ~11-12%, with the crowded moderate lane (Giannoulias, Conway, Pappas, Quigley) and her 2019 fifth-place 9% finish as the dominant negatives. I partially accept Challenge 1 (sq2 may be closer to 25% given coalition splitting) and Challenge 2 (sq3 closer to 45% given Vallas precedent of moderates losing consolidated runoffs), which would push me down to ~8-9%; but I also partially accept Challenge 3 (entry probability closer to 85%) and Challenge 4 (asymmetric upside if Giannoulias stays out), which push back up. These roughly offset, leaving me near 12-13%. The market at 16% is only 3-4 points above me with a declining trend toward my view and an anomalous orderbook reducing its signal value, so I hold near my independent estimate at 0.13.