Kurt Volker, US Department Special Representative for Ukraine speaks during a press conference about US-Ukrainian relations in Kiev. (Photo by Pavlo Gonchar/SOPA Images/LightRocket via Getty Images) Pavlo Gonchar | LightRocket | Getty Images

"We intend to initiate and complete a transparent and unbiased investigation of all available facts and episodes, including those involving Burisma and the 2016 U.S. elections," Volker and Sondland agreed that the Ukrainian president should say. Zelenskiy never did make the statement. Burisma Holdings is a Ukrainian gas company whose board Hunter Biden joined in 2014, while his father was vice president and handling the Ukraine portfolio. Trump has made unsubstantiated allegations that the arrangement was corrupt. There is no evidence of wrongdoing by either Joe or Hunter Biden. The president has also long promoted the baseless theory that Ukraine — not Russia — was responsible for 2016 election meddling. The texts also show a panicky top aide to Zelenskiy reaching out to Volker after the president unexpectedly halted roughly $400 million in military assistance to Ukraine, as he increased pressure on Zelenskiy to investigate. On August 29, Zelenskiy aide Andrey Yermak texted Volker: "Need to talk with you."