If a major party POTUS nominee discovered that he had serious but probably treatable cancer in October, would you want him to tell the American people before the election (potentially altering the outcome), or wait until after he/she won to disclose it?Hmm...that's a good one, and I'm fighting the urge to say "depends." I mean, how "probable" is probably treatable? How debilitating is the expected treatment? Is this the kind of illness where revealing it would almost certainly cost votes, or is the kind of thing that people mostly accept as no big deal? And I suppose another very practical one: how confident can the candidate be that it won't leak if it's not disclosed?
The interests to balance here, I suppose, are the responsibility to the electorate and the responsibility to the party. Both are real and serious, and yup, they seem to be in conflict here.
And...I'm going to use one of the outs I mentioned. Because calculating the proper response to the responsibility to the party has to include not only the risk to election of disclosing but also the risk to election of not disclosing and then being discovered, I think I'll say that the responsibility to party and supporters won't outweigh the responsibility to the electorate. So you disclose...at least up the last few days before the election, at which point you can also make the (dubious?) argument that revealing such a thing in the last few days may be as likely to give the candidate an unfair advantage as it is to produce an unfair disadvantage.