To put forth PfRC’s style guide at the outset, we’d use Harris’ and Walz’ campaign for the US presidency—but we are really enjoying the outbreak of pedantry over the placement of the apostrophe (see previously) for the names of the candidates and how it’s an interesting case of overlap of grammar and morphology. While conceding that in conversation I may pronounce it Harrises platform or Walzes career, I think the construction is superfluous for names ending in s, z, x, ร (the medial ลฟ is never terminal unlike the former Esszet), ch and j (as the affricatives tส, dส), though the instruction if you say it, spell it does seem like a good rule to apply to spare oneself some grief. Should Harris win (otherwise we could all be Ofdon and Ofjamesdavid—the genitive case is weird), she will become only the fourth holder of high office to have such a surname ending (the last being Rutherford B Hayes), but a more recent contender, Michael Dukakis, interviewed for the article recalled no such controversy back in 1988 and agrees it should be s, apostrophe and that’s it.