Oh, that's easy. You see people vote like this if they don't advance economically. So what you need is to create a decade or so of economic advancement for >50% of the US.

If that doesn't happen, odds are that even if a democrat president gets elected, they won't be much better. This is still the fallout of the GFC, of the decision to bail out the banks back then.

I know that sounds incredible, and I would have bitten off the head of anyone claiming this when I was 20 ... but it's how the world works.