It probably nudged the needle by a point or two but in reality Hilary should never have been that close. When you look back her campaign was very much in cruise control and they took far too much for granted. They massively underestimated how disliked the Clinton brand was outside of the Washington bubble. And they massively underestimated how much Trump was controlling the news cycle and drowning her out. You look now how carefully the Harris team act in ensuring they don't appear to be part of the Washington elite. The Walz pick is what Hillary didn't have, he brings that normal person vibe. And JD is a massive own goal on appealing to normal people.
Trump appeals to dumb ass rural voters who often don't vote and hopes that the traditional white collar gop vote will hold their nose. That was the coalition that won in 2016. His problems this time appear to be with those white collar gop voters.