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 the latest Manifold newsletter:
North Dakota: Katrina Christiansen (D) vs. Sen. Kevin Cramer (R)
Expert forecasts: Solid R (Cook), Safe R (Sabato), Solid R (Inside Elections)
Poll results (538): Cramer+22, Cramer+9, Cramer+29 (the last two are partisan polls)
Election result in 2018, a Democratic wave year: R+11 (Cramer vs. Heitkamp)
Election result in 2012, amid Obama's reelection: D+1 (Heitkamp vs. Berg)
Recent North Dakota presidential election results: Trump+33 (2020), Trump+36 (2016), Romney+20 (2012)
Commentary:
Like Indiana and Missouri, this seat was won by a Democrat in 2012 who then lost in 2018. Heidi Heitkamp’s loss was even more decisive. I don’t think anyone’s holding their breath for 2024.