Unfortunately, it's a bit too late to switch candidates now. It's an election year. Withholding our votes won't result in better candidates in the next election. In fact in this case there won't be a next election if Trump wins. We need to politically engaged for the next four years if we want a better candidate in 2028. Which I do. So I'm going to vote for Biden since he isn't going to destroy democracy for personal gain.
Biden has already won the Idaho and New Hampshire primaries. It would take a major upset or him dying to get someone else the Democratic nomination at this point.
I was hoping Biden would honor his promise to be one term president. It's clear he's not going to do that. Trump will definitely endorse genocides that will kill many more people than have died so far.