What’s the role of Kurt Volker in Trump-Ukraine saga?

At a Press conference this morning, President Trump said China (and Ukraine) should investigate the business ties of Joe Biden, his son Hunter Biden, and their dealings in Ukraine.

As Trump made this new allegation, the former envoy to Ukraine, Kurt Volker, was testifying to Congressional investigators. Volker is a possible lynchpin in all of this because he served as the go-between of Trump’s personal attorney Rudy Giuliani and Kiev.

Volker resigned from his position just a week ago, soon after being mentioned in the whistleblower complaint about Trump’s phone call with the Ukranian president.