[85] At the same time, Fruman and Parnas were being paid by Dmytro Firtash, a Ukrainian oligarch, with alleged ties to Russian organized crime and the Kremlin, who is facing federal bribery charges in the U.S. and is fighting extradition from Austria.

Zelenskyy reportedly felt rattled by the pressure, according to Amos Hochstein, a former diplomat and a member of Naftogaz's supervisory board, who alerted the National Security Council (NSC) of the matter in May 2019.

A subsequently unredacted version of the message showed that days later Parnas sent Giuliani a document that appeared to contain notes from an interview with Mykola Zlochevsky, the owner of Burisma Holdings, casting doubt on Schiff's interpretation.

[3][6] One proposed investigation would concern a conspiracy theory—which originated on 4chan in 2017 and was spread by blogs, social media, and Fox News—[112] that connected the American cybersecurity technology company CrowdStrike to Ukrainian actors supposedly interfering in the 2016 election.

Schiff argued that the complaint might have been withheld from Congress "in an unlawful effort to protect the President and conceal from the Committee information related to his possible 'serious or flagrant' misconduct, abuse of power, or violation of law".

[126] The memorandum of the conversation confirmed the whistleblower's allegations that Trump had requested investigations into the Bidens and invoked a conspiracy theory involving a Democratic National Committee server, while repeatedly urging Zelenskyy to work with Giuliani and Barr on these matters.

[126] Prominent Democrats, including Senators Robert Menendez and Chris Murphy, suggested that the hold may have been intended to implicitly or explicitly pressure the Ukrainian government to investigate Hunter Biden.

[105] Two people close to Trump told The New York Times that the behavior in the scandal was "typical" of his "dealings on the phone with world leaders", e.g. engaging in flattery, discussing cooperation, and bringing up a personal favor which then could be delegated.

[10][11] This came alongside media reports that the White House had used the most highly classified system to store memorandums of conversations with the leaders and officials of countries including Ukraine, Saudi Arabia and Russia.

Administration officials had begun storing these transcripts into this system after Trump's conversations with Australia's prime minister Malcolm Turnbull and Mexico's president Enrique Peña Nieto leaked earlier in 2017.

[225] According to Representative Gerry Connolly (D-Virginia), Kent testified that, during a meeting at the White House on May 23 organized by Mulvaney,[226] Sondland, Volker, and Perry, who called themselves the "three amigos",[185][186] had declared that they were now responsible for Ukrainian affairs.

[230] In his opening remarks, he said "[t]he timing of my resignation was the result of two overriding concerns: the failure, in my view, of the State Department to offer support to Foreign Service employees caught up in the impeachment inquiry on Ukraine and, second, by what appears to be the utilization of our ambassadors overseas to advance a domestic political objective.

According to The New York Times, this conflicts with previous testimony given during the inquiry in which other State Department officials testified that Sondland was "a willing participant who inserted himself into Ukraine policy even though the country is not in the purview of his posting, and was a key player in [Trump]'s efforts to win a commitment from the new Ukrainian government to investigate his political rivals.

Taylor testified that he had learned in mid-July 2019 that a potential White House meeting between Trump and Zelenskyy "was conditioned on the investigations of Burisma and alleged Ukrainian interference in the 2016 U.S. elections", and that he later was told, in September 2019, that U.S. military aid to Ukraine was also dependent on such investigations—including into the Bidens.

[239] Cooper's testimony, originally scheduled for that morning, was delayed by roughly five hours when a group of House Republicans led by Matt Gaetz (R-Florida) stormed the SCIF where impeachment inquiry committee meetings are being held,[240] and refused to leave, at one point ordering pizza.

[254] On October 29, 2019, the NSC's head of European Affairs, Lieutenant Colonel Alexander Vindman, testified before the House committees, stating he had overheard Trump's phone conversation with the Ukrainian President.

She added: "On July 18, I participated in a sub-Policy Coordination Committee video conference where an [Office of Management and Budget (OMB)] representative reported that the White House Chief of Staff, Mick Mulvaney, had placed an informal hold on security assistance to Ukraine.

[278] Jennifer Williams, a special advisor to United States Vice President Mike Pence on European and Russian affairs, who happened to be listening in on the July 25 call, testified on November 7, 2019.

The State Department meanwhile remained silent while she faced public attacks in an attempt to recall her to the U.S.[298] Yovanovitch had been told by Sondland that showing support for the U.S. president may help prevent her dismissal but she chose not to heed the advice.

"[306] On October 25, 2019, Charles Kupperman, Trump's former deputy national security adviser, filed an advisory lawsuit, asking a D.C. federal judge to rule on whether he is lawfully obliged to comply with a subpoena he received from the House of Representatives.

[343] The House Intelligence Committee ranking member, Representative Devin Nunes (R-California), in a November 9 letter, provided a list of eight witnesses from whom the minority party wished to hear, including Hunter Biden.

[352] Taylor testified that the day after the Trump–Zelenskyy phone call, one of his aides, David Holmes, overheard Sondland speaking to Trump via cellphone in a Kyiv restaurant, hearing the president refer to "the investigations".

[370] At the request of Republicans, former U.S. Special Representative for Ukraine Kurt Volker and former National Security presidential adviser on Europe and Russia Tim Morrison gave public testimony before the House Intelligence Committee.

[373][374] Ambassador to the European Union Gordon Sondland testified that he conducted his work with Giuliani at the "express direction of the president",[375] and that he understood a potential White House invitation for Zelenskyy to be contingent on Ukraine announcing investigations into the 2016 elections and Burisma.

[403] On September 30, CNN, citing an analysis by Laura Edelson at New York University's Tandon School of Engineering, reported that Trump and his reelection campaign had spent hundreds of thousands of dollars on Facebook advertisements to push for his defense.

[406][407] Later that same day, Mulvaney issued a statement criticizing the media for their coverage of his comments and denying his earlier remarks, reiterating there was "no quid pro quo" regarding the withheld aid and requests to investigate the Democrats' behavior during the 2016 election.

"[416] Some Trump supporters also adopted the terms "coup" and "lynching", drawing criticism from opponents who pointed out that the impeachment process was neither violent nor extralegal, and that control of the Presidency would remain with the same political party even if successful.

[441] A majority of House members voted in favor of initiation of the impeachment inquiry, including 231 Democrats, and one independent,[21][442] Justin Amash from Michigan,[443] who left the Republican Party on July 4, 2019, in the wake of his protests about holding Trump accountable.

[462] On October 23, more than two dozen Republican members of the House—led by Representative Gaetz and with Trump's prior knowledge and assent—staged a protest against impeachment proceedings by entering the SCIF where a hearing was about to commence, some carrying cellphones in violation of security protocols.

On Twitter, Harvard Law School professor John Coates cautioned that the tweet was an independent basis for impeachment as the sitting president was threatening civil war if Congress exercised its constitutionally authorized power.