Key takeaways
- Polymarket and Kalshi traders moved $5.5 million in combined volume on KY-04, with Gallrein at 52%.
- Super PACs supporting Gallrein spent more than $14 million, making KY-04 the most expensive U.S. primary ever.
- Massie is behind Gallrein by 43 to 48 percent in the polls, with the May 19 result depending on turnout.
Gallrein is ahead of Massie on Polymarket and Kalshi in Kentucky’s home race
On Polymarket, the KY-04 Republican Primary Winners Marketplace attracted $1,417,372 in total trade volume. Gallrein currently holds an implied probability of winning of 52%, with shares valued at 52.0 cents. Massie is right behind at 50%, with shares at 50 cents. Even though he trails in odds, Massie commands $999,625 in individual stocks trade volume in this market, compared to $348,815 for Gallrein.
The remaining candidates, Nicole Lee Ethington and Robert Wells Jr., each have less than 1% chance, with volumes of $39,638 and $29,315, respectively. Kalshi tells a similar story on a higher level volume. The market for KY-04 Republican candidates on this platform generated a total of $4,131,826 ahead of the May 19 primary. Gallrein leads with 52%, its “Yes” contracts trading at 52 cents. Massie follows at 49 cents, implying a 49% probability. Ethington and Wells remain below 1% on Kalshi Also.
The May 19 primary in Kentucky’s 4th Congressional District is the costliest primary on record in the United States. Ad tracking company Adimpact puts total spending on TV, radio and digital advertising at more than $25 million as of mid-May. Super PACs invested most of that money, with groups supporting Gallrein largely outspending pro-Massie efforts.
Gallrein, a fifth-generation Shelby County farmer and retired U.S. Navy SEAL captain with about 30 years of service, including time on SEAL Team Six, received Trump’s endorsement in October 2025. President Trump endorsed Gallrein after a series of public feuds with Massie over votes on foreign aid to Israel and Ukraine, government funding legislation and the handling of the Epstein cases.
Massie, first elected in a 2012 special election, built his reputation on libertarian-leaning conservatism, consistent opposition to uncontrolled spending and skepticism of foreign entanglements. He represents a district spanning northeastern Kentucky, including suburban Cincinnati and parts extending toward Louisville, where registered Republicans make up an overwhelming majority. The overall winner enters November as the heavy favorite.
Massie is well known in the crypto space and his representative has proposed legislation to abolish the US Federal Reserve. The Libertarian congressman also accepted Bitcoin (BTC) for campaign donations for this specific primary race. Campaign finance records through the end of April show Massie raised about $5.5 million and spent the majority of it.
Gallrein directly raised approximately $3.1 million. The super PAC’s portrait leans toward the challenger: Outside pro-Gallrein groups, including the Republican Jewish Coalition at about $4 million and AIPAC-affiliated organizations at about $2.6 million, have invested about $14 million or more on his behalf. Pro-Massie PACs fought back with roughly $10 million to $11 million in support.
A Quantus Insights poll conducted May 11-12 of about 900 likely voters shows Gallrein at 48 percent and Massie at 43 percent, with 8 percent undecided. Gallrein leads among women and older voters; Massie is stronger with men and younger voters. Previous polls had Massie in the lead, but sustained advertising pressure appears to have changed the numbers.
Massie campaigned alongside Rep. Lauren Boebert and framed the race as a fight against billionaire outside interest groups trying to buy a seat in Congress. Gallrein focused his campaign on military service and unconditional support for Trump’s agenda. Neither candidate has agreed to a formal debate.
The district is solidly Republican, meaning the outcome will effectively determine who fills the seat in the next Congress.
A Massie victory would show that incumbents with deep local roots and consistent election records can withstand Trump-backed primary challenges and nine-figure outside spending. Massie has successfully overcome such challenges in the past. A Gallrein victory would indicate that sustained advertising spending and presidential support can dislodge even a longtime member with a loyal base.
Polls open at 6 a.m. ET and close at 6 p.m. ET on May 19. Results are expected shortly after closing.
