How important to the impeachment inquiry is Kurt Volker?

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The impeachment inquiry moves into a new phase today as House investigators conduct a face-to-face interview with the former Special Envoy to Ukraine, Kurt Volker. Stephanie Ruhle is joined by NBC’s Jonathan Allen, former Senior Advisor to Jeb Bush Michael Steel, former Deputy Labor Secretary Chris Lu, and University of Pennsylvania Professor Claire Finkelstein to break down who Volker is and what his significance is to the impeachment inquiry.