He could/should have addressed this back in the primaries. They were running stories about it. He said nothing.

https://www.politico.com/magazine/story/2019/08/02/joe-biden...

https://www.politico.com/news/2020/03/09/james-biden-health-...

https://www.newyorker.com/magazine/2019/07/08/will-hunter-bi...

https://www.nytimes.com/2019/05/01/us/politics/biden-son-ukr...