If you order all the Senate seats by their vote margin after the election, which one would give Democrats their 51st seat? This idea was popularized by Nate Silver. If they're caucusing with Democrats, I'm counting them for this market.

For example, in the 2024 Senate elections, Montana would be the tipping point state for Democrats. If the country had voted 7.16% more Democratic across the board, Democrats would have 51 seats, with Montana being the narrowest seat they won. Note that the tipping point for Republicans would be their 50th seat, but Democrats have to get 51 seats for control of the Senate.

Feel free to add more states you think could be it!

https://en.wikipedia.org/wiki/Tipping-point_state

https://en.wikipedia.org/wiki/2024_United_States_Senate_elections#Closest_races

Possible clarification from creator (AI generated): The example in the description has been corrected - in the 2024 Senate elections, Montana would be the tipping point state for Democrats, not Nebraska.