This market is meant to be insurance for anyone trying to do arbitrage on various markets of the form of "if the election is between X and Y who will win" or "if X and Y win nominations will Z party win". These are generally speaking the same idea but they have a possible edge case where X becomes the nominee but then dies or drops out or is deemed ineligible etc before the election. In this case depending on how the question was phrased otherwise similar markets may resolve differently. So this market is asking whether something like that will happen to either the Democratic or Republican nominee after they have won the nomination.

Apr 10, 6:23pm: 2024 election black swan insurance: will a major party nominee die or withdraw before election → Will the 2024 Dem or Rep presidential nominee die or withdraw before election