I will say this debate is inherently riskier than the last one simply because JD Vance is already at his floor. He’s the most unpopular VP or VP candidate in history. Worse than Sarah Palin, worse than Spiro Agnew, worse than Aaron Burr.
He loses, nothing changes, he cannot go lower barring Mark Robinson tier revelations and even then I have doubts. He wins, Walz slips a point or two, Harris by extension maybe 1/4th of a point.

Really anything that can stop the bleed for the Republicans is a win for them, October is critical. Harris rode a 6 week high after getting in at the end of July, spent the first two weeks undoing the pit Biden had dug, then got boosts from the VP pick and convention that lasted until early September. Trump finally had trends on his side and the debate utterly wrecked that. That’s finally fading again so they really are seeking a win, a screw up here could be too late to wait out and Vance getting some good press could bury stuff like the Uncle Robinson(no relation) disaster.

The other problem is that he’s young, really young, Teddy young. JD Vance is young enough he can fake it for a little bit in a way Trump is just too old to do these days. He’s baitable, but not to the level of Trump or even Biden in this environment. Young Narcissists can put on a face for a while in a controlled space like this, 80s Trump did it all the time and I’d argue Vance might be sharper than him.

I don’t think it’s a bad matchup, Walz is very wholesome and more experienced(and the reverse would be very unideal for the Democrats. Vance would be better at avoiding the massive tangents Harris baited Trump into, meanwhile Walz isn’t as high energy or effective on the pursuit against Trump as Harris is) , but he definitely ‘looks’ and ‘sounds’ older than he is, especially compared to Harris. So Walz is walking in with that already there.

The last thing anybody wants is Trump pulling it out and calling all the headlines lies. Surprised Biden never did actually

Just FYI so you don’t get ‘gotchaed’, Trump isn’t the oldest nominee ever. Neither was Biden. Record is still held by Peter Cooper from the reconstruction era who was 84 when nominated.