RFKjr did say 34% wins, but that's the best case minimum where the other candidates split the remaining 66% such that none exceed 33%.  But if, as polls suggest now, that Trump has a 10 point lead on Biden,  Trump could win with 38 to Biden's 28.  There are 32 such splits (taking only whole number splits) that could occur in which 34% doesn't win.

Also third party candidates tend to fade off their best polls toward election day.
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I think he could have a major impact, but winning outright is pretty remote.