I can't tell if Luntz is actually hinting at anything or just saying that there is always another Trump scandal popping up.
Unless it's something like the N word, I don't know what will hurt him. The sexual comments are already out there, so more of those won't do much. Talking about Russia/Putin? Most Americana are more outraged by sex/bad language I would think.
Things that would actually hurt him at this point, IMHO:
*he's broke
*he's flat-out embezzling money from his campaign (more than he already is)
*he paid for an abortion for a mistress
*one or more videos of him gving insane racist or misogynistic rants
*video of him committing sexual assault (possibly against a minor)
*video/audio (maybe email?) of him conspiring with the Clintons or Russia
*he funded the 9/11 hijackers (likely unwittingly)
Only being broke and 9/11 profiteering will honestly hurt Trump among his base and the "Independents" enough to dissuade them from voting, but both of those can never be proven since his tax returns will never be released or (wiki)leaked.
All of the rest of the scandals will have minimal impact. Indeed, the sex scandals alone can be -- have been already -- minimized as the quaint peccadilloes of an aging Wall Street playboy.
