The Most Expensive Primaries in American History — and What the Money Actually Bought

Michigan 2026 just set the all-time record for a Senate primary. A tour through the priciest intra-party wars ever waged shows a pattern donors keep refusing to learn.

Somewhere in the final week of Michigan’s Democratic Senate primary, the race quietly crossed a line no American primary had crossed before: with outside spending alone reaching roughly $65 million, it became the most expensive Senate primary ever conducted. The distinction of costliest intra-party fight in history now belongs to a race the money side lost. That outcome is less anomalous than it sounds. Walk through the biggest-spending primaries of the modern era and a consistent, uncomfortable pattern emerges: past a certain threshold, primary money stops buying votes and starts buying backlash.

The record book

Michigan Senate, 2026 (D). The new champion. Roughly $65 million in outside money, more than $30 million of it from AIPAC-aligned groups backing Haley Stevens, plus a several-fold airwave advantage — against which Abdul El-Sayed won by a point. The spending itself became El-Sayed’s closing argument, folded into his anti-corporate-money message. The lesson practically writes itself.

NY-16, 2024 (D). The previous cautionary tale — the most expensive House primary in history, in which AIPAC’s super PAC arm led an eight-figure campaign that successfully unseated Rep. Jamaal Bowman in favor of George Latimer. The money side won that one, which is precisely why Michigan was funded so confidently: the playbook had a track record. What changed between a Westchester House district and a statewide Michigan electorate is the subject of a separate post — but scale, candidate quality, and a mobilized community were the short answer.

Pennsylvania Senate, 2022 (R). The self-funding derby. Mehmet Oz and David McCormick poured personal fortunes into a race ultimately decided by about a thousand votes and a Trump endorsement — tens of millions of dollars to a photo finish settled by a single tweet-length statement. Rarely has the marginal value of a dollar versus an endorsement been measured so precisely.

Ohio Senate, 2022 (R). The donor-primary prototype: a crowded field, super PACs aligned with individual billionaires — most famously the eight-figure bet behind J.D. Vance — and a result that arguably proved money can work, when it is spent lifting an unknown rather than destroying a known. That distinction recurs across the record book like a law of physics.

Why primaries break the money machine

General elections reward saturation because they are fought over low-information marginal voters choosing between parties. Primaries are the opposite environment: higher-information electorates, no party heuristic, and — crucially — an available counter-narrative in which the spending itself is the villain. Every dollar past the saturation point strengthens the underfunded candidate’s best argument. Michigan supercharged the effect because El-Sayed’s entire platform was already about money in politics; his opponents effectively spent $65 million producing evidence for his thesis.

There’s a second mechanism, subtler and more modern: negative saturation now travels with receipts. Voters in 2026 see spending totals in their feeds alongside the ads themselves. The FEC-report screenshot is a genre. Opacity was always half of outside money’s power, and it is gone.

The forecast

None of this means the era of mega-primaries is ending — the opposite. Donor networks on both sides absorbed 2026’s lesson not as “spend less” but as “spend differently”: earlier, more positive, more digital, more disguised. The record set in Michigan will fall, probably by 2028, possibly in a presidential primary context that makes $65 million look quaint. What Michigan permanently changed is the mystique. The next candidate staring down an eight-figure avalanche has something no such candidate had before: proof, at the highest possible profile, that the avalanche can be survived — and even surfed.