https://www.google.com/amp/s/www.wsj.com/amp/articles/timeline-of-trump-ukraine-bidens-story-11569095501
Calling for the firing of the prosecutor investigating the company your son is working for and threatening to hold up aid over it is clear as day blatant corruption. If for example it was found that President Trump called for Vladimir Putin to fire a Russian prosecutor investigating a Russian oil company for corruption otherwise US aid money would be withheld and it just so happened that Don Jr. was on the board of directors, Trump would be removed from office, I guarantee it. You can argue whether Hunter was corrupt or if he was even on Ukraine’s radar, but Joe knew. Hunter had had that job for some time, so unless Joe and Hunter never talked at all during that time, Joe would definitely have known where his son was working.