In two paragraphs sent to House investigators Tuesday, President Trump's personal lawyer Rudy Giuliani rebuffed a Congressional subpoena to testify in impeachment investigations and provide documents to three committees.
Here is a timeline of the events leading to and following that decision.
Giuliani's business dealings have reportedly come under the scrutiny of federal prosecutors, while two of his associates were arrested last week on campaign finance charges.
Democrats began the impeachment inquiry on September 24 following the disclosure that the whistleblower had lodged a complaint about a July 25 phone call in which Trump pressed Ukrainian President Volodymyr Zelenskiy to investigate Biden, a leading contender for the Democratic nomination in 2020, and his son Hunter, who had business interests in Ukraine.
Texas Rep. Michael McCaul, who is the top Republican member on the House Foreign Affairs Committee, said of Giuliani when asked if he had concerns: "I know he's been subpoenaed for documents, and I fully anticipate he's going to be subpoenaed as a witness".
Kent, who has spent much of his career fighting corruption in Ukraine and elsewhere, is the second career diplomat to testify as part of the probe.
On Monday, former senior White House Russia aide Fiona Hill testified that she had tried to raise the alarm about possibly illegal activity - and had been encouraged to do so by Bolton.
Hill quoted Bolton, whom Trump forced out last month, as saying in one conversation that Giuliani was "a hand grenade who's going to blow everybody up".
Career State Department official George Kent testified Tuesday he was told by administration officials to "lay low" on Ukraine as "three amigos" tied to the White House took over US foreign policy toward the Eastern European ally.
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In the letter to attorney Lee Wolosky, White House Deputy Counsel Michael Purpura cited the doctrine of executive privilege, which is meant to protect communications between the president and close advisers to ensure candid, private advice.
A parade of USA diplomats will head to Capitol Hill for closed-door testimony this week as Democrats build their impeachment case against President Donald Trump, while the White House considers ways to slow down the process.
It's not clear when the House will hold the vote on authorizing the inquiry.
While interviews have focused on the interactions with Ukraine, the probe could broaden as soon as next week to include interviews with White House budget officials who may be able to shed light on whether military aid was withheld from Ukraine as Trump and Giuliani pushed for the investigations.
Democrats have accused Trump of pressuring a vulnerable US ally to dig up dirt on a domestic rival after withholding $391-million in USA security aid meant to help combat Russian-backed separatists in the eastern part of Ukraine.
The Trump administration has refused to cooperate with House lawmakers, and have said the investigation is illegitimate until a vote is held. Mr Trump eventually allowed the aid. Trump faces allegations he threatened to with hold almost $400 million in funding unless the Ukraine agreed to launch an investigation into Joe and Hunter Biden.
Michael McKinley, former Senior Advisor to the Secretary of State, arrives for his deposition amid the U.S. House of Representatives' impeachment inquiry into President Trump in the US Capitol in Washington, D.C., on October 16 2019.
Requested whether or not she ought to maintain a vote to name Trump's bluff, Pelosi mentioned: "This is not a game for us".
Yovanovitch on Friday denied Giuliani's allegations that she provided a "do not prosecute list" to Ukrainian officials to protect Biden and others.
Trump has denied wrongdoing and defended his request to Zelenskiy during the phone call, which prompted a formal whistleblower complaint by an individual within the US intelligence community.