Also important to know, if democrats take back the house, Johnson would no longer be speaker at the time the presidential election is certified. It’s the next congress, not the current one, that will certify the vote. New congress is seated on January 3rd 2025, and the presidential election certification is on January 6th 2025.
Polling errors are not predictable beforehand. If they were, we wouldn’t have polling errors. In 2022 for instance there was polling error in favor of democrats not against (or at least too much emphasis on polls with errors in Republican favor).
https://www.nytimes.com/2022/12/31/us/politics/polling-election-2022-red-wave.html
We can’t know the electorate beforehand, so poll weighting and deciding who is a likely voter is always going to involve some guesswork. So the opposite of what you say is true as well, if there is a small polling error that overstates Trump’s support it would have Kamala sweeping every swing state.
But the polls show a close election, all we can do is do our best to do things that help her win. Like voting early to make sure our vote gets in no matter what, encouraging people we know to register and vote, volunteering, canvassing, donating, etc.