As much as I appreciate the idea behind @NathanpmYoung's market on conditional victory probabilities, it suffers from the spurious counterfactual problem: if everyone knows a candidate won't be selected, then the conditional market will resolve N/A, so there's no incentive for sharp traders to push back against activist traders. So here's a market where exactly one option will win.

My criterion for the identity of the ticket is the pair that appears on ballots in at least 40 of the 50 US states; if there is no such pair, I will resolve N/A. My criterion for whether the Democrats win or lose the election is whether a Democrat or a non-Democrat is inaugurated on January 20, 2025; if neither occurs, I will resolve N/A. If either the Democratic or Republican ticket concedes before then (and no third party has secured enough electoral votes to matter), I will resolve early based on that.

If you add another option for VP, I ask that you make a pair for win and loss, and format them like the above. (Note that there are already options for "Harris is not the nominee"; if you want to break that possibility down further, please create another market).

The conditional market, for comparison: