And now, according to a cache of text messages released on Thursday, top United States diplomats encouraged Ukraine's newly elected president Vlodyrmyr Zelensky to investigate Joe Biden's family in return for a potentially high-profile visit to Washington with President Donald Trump.
The messages, released by House Democrats, show former USA special envoy to Ukraine Kurt Volker writing to top Zelensky aide Andrey Yermak, promising the new Ukrainian leader a trip to Washington in exchange for the investigation.
Democratic leaders subpoenaed the White House in a wide-ranging request for information about Trump's actions in the Ukraine controversy.
Secretary of State Mike Pompeo publicly acknowledged this week that he was on the July 25 call between Trump and Zelenskiy, and that disclosure put a spotlight on his previous attempts to distance himself from the issue.
He was labeled "was one of the administration's 'three amigos' on Ukrainian policy, along with Kurt Volker, the US special representative for the Ukraine conflict, and Gordon Sondland, the USA ambassador to the European Union".
Pence also appeared in the whistleblower's complaint, with the US intelligence official claiming that on or around May 14, Trump instructed Pence to cancel a planned trip to Ukraine to attend the inauguration of Volodymyr Zelenskiy, the new Ukrainian president, on May 20.
But Perry told an evangelical Christian news outlet, CBN News, in an interview aired Friday that he had never heard anyone in the administration bring up Biden or Biden's son, who served on a board of a Ukraine natural gas business, in dealings with Ukrainian officials.
Trump's personal lawyer Rudy Giuliani told The Journal that he advised the president that there were complaints among his supporters that Yovanovitch privately harbored an "anti-Trump bias".
In a statement Thursday, Joe Biden called Trump's remarks "a grotesque choice of lies over truth and self over the country".
"Russia, if you're listening, I hope you're able to find the 30,000 emails that are missing", Trump said during a July 2016 press conference.
They came from Volker, who testified behind closed doors Thursday after resigning last week.
Perry, the former governor of Texas and up to now a lower-profile but active member of Trump's Cabinet, has made repeated trips to Ukraine and met often with Ukranian officials, including Zelenskiy.
It also would have called for the Ukrainian government to look into unsubstantiated conspiracy theories suggesting that it was not Russian Federation, but Ukraine that interfered in the 2016 election, and that it did so to help then Democratic nominee Hillary Clinton.
"President Trump is under the misimpression that if he keeps committing impeachable offenses, he can somehow normalize them and escape accountability", advocacy group Public Citizen said in response to the president's comments.
The Prosecutor General's Office said in a statement that among the cases being reviewed are 15 in which Zlochevsky is mentioned.