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United StatesIn the previous issue, the Republican side of both control contracts had not moved a single time. This week both of them moved, and in opposite directions. The Republican House contract went from 11.50% at the Sep 4 close to 13.50% at the Sep 11 close, touching 14.50% on Sep 10 along the way, the top of the series that began on Jul 29. The Republican Senate contract did the opposite and went from 49.50% to 48.50%.
The difference from the previous week is what remains once the pair is normalized. In the Senate the pair summed to 101.00% at both ends, so the point left one side and entered the other: -0.99pp normalized for the Republicans and +0.99pp for the Democrats. That is a transfer, not the book widening. The order was recorded: the Republican leg shows 48.50% at the 08:00 UTC reading on Sep 8, and the Democratic leg rises to 52.50% at the 11:00 UTC reading. In the House the pair widened from 100.00% to 101.00%, and even so the Republican move survives almost intact: +2.00pp raw, +1.87pp normalized.
The finding of the week is in the Senate seat distribution, and it is a finding about size. Adding up the bands in which the Republicans control the chamber, 50 seats and above, and normalizing by the sum of the table, the probability of Republican control fell from 45.46% to 40.43%, a loss of 5.03pp. The binary contract, which answers the same question, lost 1.00pp. The distance between the two books doubled, from 4.04pp to 8.07pp, and it doubled because the distribution moved five times as much as the binary did. The sum of the eleven bands barely changed, 98.10% and 98.20%, so what happened was mass shifting between bands: 4.20pp left the band of exactly 52 seats, and the three bands of 49 seats or fewer gained 5.00pp.
The money ran in the opposite direction to the size of the move. The whole distribution took in USD 11,573 of new money between the two closes. The Senate binary took in USD 133,896, and the House binary USD 813,478, 84% of everything that entered the eight midterm contracts. The largest move of the week came from the book with the least new money.
The week had two Senate primaries. In New Hampshire, on Sep 8, Chris Pappas won the Democratic primary and John Sununu the Republican one, for the seat Jeanne Shaheen is leaving. In Rhode Island, on Sep 9, voters cast ballots for Jack Reed's seat. The Senate binary shifted level at the 08:00 UTC reading on Sep 8, hours before the New Hampshire count. AFOS records the dates and does not claim a link between them.
1.Executive Summary
For a desk, this week reverses the reading of the previous one. In issue №7, half of the raw Senate move was the book widening. In this one, the moves in both binaries survive normalization. In the Senate, entirely: the pair stayed at 101.00% and the point passed from one side to the other. In the House, with room to spare: the Republican side rose 2.00pp raw and 1.87pp normalized, on USD 813,478 of new money in the book.
The largest move of the week was not in the binaries. It was in the Senate seat distribution, which took 5.03pp off the probability of Republican control while the binary took off 1.00pp. The two books answer the same question by different routes, and the distance between them doubled to 8.07pp.
What weighs on the reading is the flow. The distribution made the largest move with USD 11,573 of new money; the House binary moved 1.87pp with seventy times as much. The two Senate books now disagree by 8.07pp, and the measurement tells how much money each of them used to reach its own price. It does not tell which of the two is right.
2.Why this brief does not subtract the market from the poll
This brief publishes two numbers about the same election and never subtracts them. The two magnitudes below do not share a unit, and the difference between them is not a number with meaning.
<strong>Why it matters:</strong> 87.50 minus 5.09 is 82.41, and that number does not exist. It has no unit, it would change size if the poll were expressed on another scale, and it corresponds to nothing that can be checked on November 3. And the gap between votes and seats is not theoretical: in 2012 the Democrats won more House votes nationwide and ended up with fewer seats. The lead in votes can grow without control changing, because the geography of the vote decides what the national sum hides.
Inside the market itself there is a pair of numbers that can be set side by side, and it is in the Senate. The binary pays 48.50% on Republican control. The seat distribution gives another number for the same question, provided a rule that is not written in the table is applied: a 50-seat tie counts as Republican control, because the vice president breaks ties. Adding the 50-seat band to the bands of 51 and above gives 39.70%, and normalizing by the sum of the eleven bands gives 40.43%. Without the rule, the calculation would use only the bands of 51 and above and the distance would come out at 20.29pp, two and a half times the real one. That is why the two books are comparable in the Senate and not in the House: there the control threshold falls on a border between bands, and in the House it falls inside the band of 215 to 219 seats, which contains 218. This is a fact about how the contracts were cut, permanent and independent of the election. What changes from week to week is the distance, which in this issue was 8.07pp.
3.Weighted scenarios for the week
The three scenarios below are not narrative: they are a direct reading of the Senate seat distribution, the contract in which the market publishes the probability of each band. The values are from the Sep 11 close, the last session of the covered week, and the eleven bands sum to 98.20%, inside the 95 to 105 gate that AFOS requires to publish a distribution. The changes start from the Sep 4 close, when the sum was 98.10%. The three scenarios cover the entire sum, with no overlap and no gap. The percentages are the market's, not the writer's, and do not constitute a recommendation.
The Republicans end up with 49 seats or fewer. It is the sum of three bands: 29.50% at 47 or fewer, 15.50% at exactly 48 and 13.50% at exactly 49. This aggregate gained 5.00pp since the Sep 4 close, with 3.00pp in the band of 47 or fewer and 2.00pp in the band of 48, while the band of 49 stood still. In this case the Senate changes hands, and the House, which the market gives the Democrats at 87.50%, follows.
The Republicans end up with 51 seats or more and govern without depending on the tiebreak. It is the sum of seven bands, from the 51-seat band at 10.50% to the band of 57 or more at 0.80%. The aggregate gave up 4.40pp, and almost all of it came from a single band: the band of exactly 52 seats fell from 8.60% to 4.40%. The band of 53 rose 0.40pp and the band of 54 gave up the same, and the other four added up to -0.20pp.
The Republicans end up with exactly 50 seats and the tiebreak goes to the vice presidency. It is the scenario that the binary counts as Republican control and that the distribution isolates in a band of its own. It gave up 0.50pp, from 12.50% to 12.00%. Because the outright majority shrank more, the tie now weighs more within Republican control: 12.00 of 39.70, three in every ten scenarios.
4.Indicator Grid
| Contract | Current | Δ week | Vol USD acc. | Implied reading |
|---|---|---|---|---|
| House, Democratic control | 87.50% | -1.00pp | USD 6.22M | Normalized by the pair, which widened to 101.00%, the drop is 1.87pp. The House book took in USD 813,478 of new money, the largest flow in the grid. |
| House, Republican control | 13.50% | +2.00pp | USD 4.67M | Touched 14.50% on Sep 10, the top of the series since Jul 29, and closed Friday one point lower. Range of 2.00pp across the 33 readings from Sep 7 to 11, with USD 325,472 of new money. |
| Senate, Democratic control | 52.50% | +1.00pp | USD 2.51M | Rose at the 11:00 UTC reading on Sep 8 and did not leave 52.50% again through Friday. With the pair steady at 101.00%, the normalized gain is 0.99pp, with USD 69,755 of new money. |
| Senate, Republican control | 48.50% | -1.00pp | USD 1.75M | The first leg to give way, at the 08:00 UTC reading on Sep 8, after 29 motionless readings in the previous week. It took in USD 64,141 of new money. |
| Senate, 47 Republican seats or fewer | 29.50% | +3.00pp | USD 0.19M | The most likely band in the distribution and the one that gained the most this week, with USD 2,699 of new money. |
| Senate, exactly 52 Republican seats | 4.40% | -4.20pp | USD 0.60M | The largest drop in the entire grid. It is the second most traded band in the distribution by accumulated volume, and it lost 4.20 of the 8.60 points it had with USD 2,512 of new money. |
| Senate, exactly 48 Republican seats | 15.50% | +2.00pp | USD 0.05M | The second largest band gain in the distribution, with USD 613 of new money. |
| Senate, 50-seat tie | 12.00% | -0.50pp | USD 0.13M | The band that the binary counts as Republican control and that the distribution isolates. It now weighs 12.00 of the 39.70 points of Republican control in the table. |
| The election happens on schedule | 97.30% | +0.50pp | USD 0.40M | Range of 0.10pp across the 28 readings from Sep 7 to 11, between 97.20% and 97.30%. A small contract by volume and the most stable in the grid by level. |
5.Liquidity and market structure
The anomaly this week is not in the ranking, it is in the flow. The eight contracts took in USD 969,224 of new money between the Sep 4 and Sep 11 closes, and 84% of it went to the House binary, where the normalized price moved 1.87pp. The band of exactly 52 Republican Senate seats, the second most traded in the distribution with USD 0.60M accumulated, made the largest move in the whole grid, 4.20pp, on USD 2,512. And the fifth row is the same as it has been since July: the 54-seat band, the most traded in the distribution with USD 0.78M, is priced at 3.60%. Accumulated volume is trading history, not current conviction, and the size of the flow is part of the reading of every number in this issue.
6.Electoral calendar through November
| Date | Sample | Why it matters | |
|---|---|---|---|
| Tue, Sep 15 | Delaware closes the primary calendar | 1 Senate seat, last state | Chris Coons's seat and the last primary on the 2026 calendar. It ends September's four Senate primaries, and from then on the grid is read with no primary scheduled until November. |
| Tue, Nov 3 | General election | 435 House seats and 1/3 of the Senate | The date on which every contract in this grid resolves. Until then AFOS measures the distance between the price and the yardstick. |
There is no mandatory poll registry in the United States, so this calendar is one of ELECTORAL EVENTS and not of release dates. Each pollster sets its own cadence. The New Hampshire primary, on Sep 8, and the Rhode Island primary, on Sep 9, took place within the covered week and leave this list. In New Hampshire, Chris Pappas won the Democratic primary with 65% and John Sununu the Republican one with 68.5%, for the seat Jeanne Shaheen is leaving. Rhode Island voted on a Wednesday because the Tuesday was the day after Labor Day. The dates are recorded and AFOS does not claim a link between them and the prices.
7.Watch list, week triggers
- The distance between the two Senate books, at 8.07pp at Friday's close doubled from 4.04pp on Sep 4, and it doubled on the distribution side: the Republican control implied by the distribution fell 5.03pp, and the binary's fell 1.00pp. If next week gives back the distribution's move without touching the binary, the distance will have been band shifting. If it stays, the two books start giving different sizes to the same outcome.
- The Republican House leg, at 13.50% after touching 14.50% is the move that survives normalization with the most room in this issue, +1.87pp, and it came with USD 813,478 of new money in the book. The pair is at 101.00%. If it closes back to 100.00% on the Democratic side, the Republican move stays whole; if it closes on the Republican side, part of it was the sum.
- The band of exactly 52 Republican Senate seats, at 4.40% made the largest move in the grid, -4.20pp, on USD 2,512 of new money against USD 0.60M accumulated. On its own it accounts for 4.20 of the 4.40pp that the outright Republican majority scenario lost.
- Delaware, on Sep 15, the last primary on the calendar closes September's four Senate primaries. In the two weeks with a Senate primary so far, the Senate binary shifted level: on Sep 2, one day after Massachusetts, and on Sep 8, the day of New Hampshire. AFOS records the dates and does not claim a link between them.
- The popular vote margin contract, structurally outside the gate its fourteen bands sum to 151.30% in the Sep 13 reading, because the contract includes a bucket that captures any other outcome and is counted along with the rest. That is how it was built, not a one-day fluctuation. It is the only market that would measure the same magnitude as the poll, and that is why it is still collected every day, to keep the series. It is never published as if it were valid.
8.Methodology
AFOS reports the three signals separately: prediction market price, generic ballot polls with sample and field dates, and press coverage from a fixed list of outlets. It does not build a composite index and does not subtract one magnitude from another.
Every published price goes through two independent readings eight minutes apart, and it only goes out when they agree within 0.20pp. The most recent reading with an approved verdict is from Sep 13, 17:13 BRT. The changes in this issue start from the Sep 4 CLOSE, the last one the previous issue published, and run to the Sep 11 close, so that every price move belongs to exactly one issue, including what happens between Friday and Monday. The close is the last point recorded in the day, with the day counted in UTC, and new money uses the same two boundaries. When the text gives a range and a number of readings, the calculation covers every point recorded from Sep 7 to 11. The House series begins on Jul 29, 2026 and the Senate series on Apr 14, 2026, so any superlative about them is always 'of the series', with the start date, and never 'of the cycle'.
When the two sides of a binary contract do not sum to 100, this brief publishes the raw and the normalized value side by side, because the difference between the two is exactly what distinguishes a point that changed hands from a point that appeared in the sum. A distribution is only published if its bands sum to between 95% and 105%. In this issue the Senate distribution sums to 98.10% at the Sep 4 close and 98.20% at the Sep 11 close, and the three scenarios in section 3 cover the second sum in full. The distance between the two Senate books normalizes the distribution by the sum of its bands and counts a 50-seat tie as Republican control. The generic ballot average is a simple arithmetic mean, with no weighting and no pollster excluded; when the same pollster publishes more than one sample from the same round, only one enters, by the hierarchy likely voters, registered voters, adults. Accumulated USD volume is cited as context and is not guidance; order book depth is not cited, by editorial decision of May 21, 2026. Code and method are open under Apache 2.0.
9.Additional reading · macro coverage
AFOS is the primary source of this analysis. The references below are complementary context reading and do not support any of the measurements above.
- ABC News · Report from Sep 8 on the fight for control of the Senate, which the article describes as open after Republicans had considered it safe., abcnews.com/Politics/wireStory/gop-confident-keeping-senate-majority-now-fight-control-136263600
- The Hill · The House Republicans' campaign arm adds five candidates to its program for competitive districts, on Sep 8., thehill.com/homenews/campaign/6076861-house-republicans-campaign-arm-adds-5-candidates-to-battleground-program/
- NPR · A roundup of the political week published on Sep 12, including the Republican midterm convention., www.npr.org/2026/09/12/nx-s1-5965782/week-in-politics-trump-attends-republican-midterm-convention-and-pentagons-9-11-memorial-service
- NBC News · Remarks by James Blair, the president's political adviser, on Republican expectations for November, published on Sep 12., www.nbcnews.com/politics/2026-election/trump-james-blair-cautiously-optimistic-midterms-scoop-podcast-rcna596830
- CBS News · A list of the November races to watch, published on Sep 13, after the week covered by this issue., www.cbsnews.com/news/2026-midterm-election-races/
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