A couple of things I think. For the Democrats Harris was never tested nationwide. I think that was a huge thing in people not knowing a ton about her and what they did know they did not like. Other issues that they overlooked were things like how she had to read a script, she was never available for interviews, and the economy really did matter even if they left that the economic numbers looked good. People do not feel like the economy is well.
For the Republicans, if they can hold the House, this would be a huge statement by the American people about what they think and feel. This election esp. the Presidency was supposed to take days to figure out not be decided the night of. Trump made incredible inroads across the board.