I would start with:
Vice President Biden, I know you’ve maintained that your son’s involvement with Burisma in Ukraine was completely legitimate, but being that you were appointed the Czar of US-Ukrainian interaction by President Obama himself, and Burisma was run by a suspected criminal under investigation by their government - How is it not, at the very least, completely irresponsible to allow such an appearance of corruption to occur, and how does such a cavalier approach to internal Ukrainian politics not disqualify you to be President?
Now that’s just mean! :D