Will eventually resolve to the party which won the popular vote for the race, as determined by the local, state, and ultimately federal governments.
In the case the race is called by the major news organizations, the market may optionally resolve early.
This market covers events up to and including Election Day, November 5: if Party A's candidate X wins the popular vote that day, but intervening events cause the next inaugurated Senator to be from Party B, the market will resolve to Party A.
If candidate X switches party affiliations, the switch will not affect the outcome if it is after the beginning of Election Day, local time.
From my latest Manifold newsletter:
Missouri: Lucas Kunce (D) vs. Sen. Josh Hawley (R)
Expert forecasts: Solid R (Cook), Safe R (Sabato), Solid R (Inside Elections)
Poll results (538): Hawley+8, Hawley+12, Hawley+5, Hawley+4, Hawley+4, Hawley+15
Election result in 2018, a Democratic wave year: R+6 (Hawley vs. McCaskill)
Election result in 2012, amid Obama's reelection: D+16 (McCaskill vs. Akin)
Recent Missouri presidential election results: Trump+16 (2020), Trump+19 (2016), Romney+10 (2012)
Commentary:
Claire McCaskill’s victory in this seat in 2012 is a remarkable story, which she wrote up here. It begins “It was August 7, 2012, and I was standing in my hotel room in Kansas City about to shotgun a beer for the first time in my life. I had just made the biggest gamble of my political career—a $1.7 million gamble—and it had paid off. Running for reelection to the U.S. Senate as a Democrat from Missouri, I had successfully manipulated the Republican primary so that in the general election I would face the candidate I was most likely to beat. And this is how I had promised my daughters we would celebrate.”
But despite her popularity, she lost in 2018 to Josh Hawley, who became the first senator to say he’d object to certifying Joe Biden’s 2020 victory. He’s generally considered somewhat far-right. His 2024 opponent, Lucas Kunce, has run for office before, but never won. He’s an attorney, veteran, and national security director for the American Economic Liberties Project. While Missouri has the potential to be more competitive than the other races in this category — The Hill has Kunce’s chances at 8% — I’d trust Manifold’s 4% more. My prediction: Hawley will win by greater than his 2018 margin against McCaskill.
@Conflux 4-8% sounded reasonable before the latest news (Lucas Kunce was at a shooting range and hit a journalist with shrapnel.)