Only publicly posted endorsements count (e.g. to ACX).
To be clear, this resolves YES if any endorsement is made in the primary or in the general election. Any presidential endorsement (as long as it's not private, or an obvious joke, or otherwise opposed to the obvious spirit of this market) for the 2024 election results in a YES.
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I'll avoid voting in this one because I'm terrified of ambiguous resolutions (and the word "endorse" is just asking for it...), but for the record I'm surprised that the probability is above 50%.
I'm also surprised that nobody's asked how an "anything but Trump" endorsement would resolve this market! I'm open to suggestions, but I think it's reasonable to resolve YES there (assuming that it happens after Biden is the democratic nominee). Another option is to resolve PROB, based on a reasonable estimate of how many people who read the vote Biden instead of a 3rd party. (That would most likely be something like PROB 95%.)
@ScottLawrence No, wait! I answered the "anybody but Trump" question already in that market! My previous answer stands, and I'm sorry for the confusion. As I said there: "No. Needs to be an endorsement of a specific candidate."
@ShakedKoplewitz By itself, no. If the word used isn't "endorse", it's gotta be something phrased as a serious recommendation for how "you should" vote.