The Ukrainian officials arrived at the White House on July 10 hoping to cement their country’s relationship with the United States, solidifying support the Trump administration seemed reluctant to extend for reasons they didn’t fully understand.

Instead, they walked into a White House that was on the verge of a crisis over Ukraine, as a simmering conflict between the president’s political impulses and the nation’s security priorities was about to erupt in the West Wing.

In a pair of volatile meetings, senior White House officials, including then-national security adviser John Bolton, were confronted with the outlines of a scheme they had previously only suspected: President Trump was seeking to use the power of his office to pressure Ukraine to deliver damaging information on former vice president Joe Biden and his son.

The Fix's Amber Phillips explains what a "quid pro quo" is and how it factors into the impeachment inquiry of President Trump. (The Washington Post)

One of the officials Trump had entrusted to pursue this agenda, Ambassador to the European Union Gordon Sondland, was undeterred by the fierce opposition from Bolton and others. He persisted in pressing Ukraine to commit to Trump’s demands, convening a second meeting even after a spectacular blowup in the West Wing.

All of this played out before the confused officials from Ukraine, who came seeking to strengthen their standing with Trump and ended up witnessing events that are now at the heart of the House impeachment inquiry.

Details of the July 10 sequence, which Bolton likened to an illicit “drug deal,” have emerged from witnesses’ testimony before House lawmakers over the past several weeks.

The Fact Checker unravels what happened when Trump tried to force an investigation into the false rumor about then-Vice President Joe Biden and Ukraine. (The Washington Post)

The most recent account came Tuesday from Army Lt. Col. Alexander Vindman, the top Ukraine adviser at the White House, who witnessed the meetings and listened to the subsequent phone call between Trump and Ukrainian President Volodymyr Zelensky.

“The Ukrainians saw this meeting as critically important in order to solidify the support of their most important international partner,” Vindman said, according to a copy of his opening statement released to the public.

But after seeing Sondland outline political demands that Trump would reiterate in his July 25 call, Vindman said, he became worried that what he had witnessed was improper, imperiled Ukraine’s ability to withstand Russian aggression and “would all undermine U.S. national security.”

The July 10 meetings have become a focal point for congressional investigators in part because Sondland articulated a seeming quid pro quo — a Zelensky visit to the White House in exchange for investigations beneficial to Trump — before a room full of witnesses, providing evidence that elements within the administration were working to pressure Ukraine well before the Trump-Zelensky call.

The reactions of Bolton, Vindman and others also underscore the extent to which even those who worked in the White House were deeply disturbed by conduct that triggered an extraordinary whistleblower complaint against the president and set in motion the impeachment inquiry.

The West Wing meetings on July 10 increasingly appear to mark the moment of detonation of the Ukraine crisis inside the White House, though by then Bolton, Vindman, then-White House Russia adviser Fiona Hill and others had become suspicious that Trump was pursuing a secret agenda.

Among the early troubling signs were the abrupt removal of the U.S. ambassador to Ukraine, Marie Yovanovitch; public statements by Trump’s lawyer, Rudolph W. Giuliani, making clear that he was pushing Ukraine to revive investigations that would hurt Democrats; and the refusal of Sondland and others to coordinate their interactions with Ukraine with regional experts at the White House and the State Department.

At the same time, officials in Kyiv were struggling to decipher conflicting signals from the Trump administration after Zelensky’s victory in the May election. Acting U.S. ambassador William B. Taylor Jr. sought to reassure the incoming Ukrainian government that it had the full support of the United States, while Sondland and others, including the special adviser on Ukraine, Kurt Volker, were putting murky conditions on the relationship.

In a conversation with Taylor and Sondland, Volker said he planned to use a July 2 meeting in Toronto with Zelensky to tell Ukraine’s president that “Trump wanted to see rule of law, transparency, but also, specifically, cooperation on investigations to ‘get to the bottom of things,’ ” Taylor said in his testimony this month.

The latter phrase appears to refer to Trump’s desire to have Ukraine pursue investigations that would help him politically, including by lending legitimacy to conspiratorial claims Trump has embraced that Ukraine interfered in the 2016 election and has hidden evidence that would implicate Kyiv.

It was against this backdrop that two of Zelensky’s senior advisers arrived at the White House on July 10: Andriy Yermak, who frequently engaged with Sondland and other U.S. diplomats; and Oleksandr Danyliuk, the head of Ukraine’s national security and defense council.

The two were ushered into a meeting in Bolton’s office in the West Wing along with Sondland, Volker, Hill, Vindman and others, according to witness accounts. The American team was working through standard U.S.-Ukraine talking points, including the United States’ desire to see Kyiv crack down on corruption, when officials familiar with the meeting say Sondland went off script.

Sondland turned the conversation away from ongoing corruption probes to reviving specific investigations that were important to Trump, according to testimony from Hill and Vindman. Although the remark was cryptic, they understood Sondland to be reflecting Trump’s desire to see Ukraine train its investigative resources on an energy company, Burisma, that had hired Hunter Biden, the former vice president’s son, to serve as a board member for about five years.

Bolton was so alarmed by the exchange that he ended the meeting abruptly and ordered those gathered out of his office, officials said. As the group filed out, Sondland instructed the Ukrainians to follow him to the Ward Room, a space in the basement of the West Wing used for meetings by national security officials.

After huddling briefly with Hill, Bolton instructed her to follow the group downstairs and monitor Sondland. There are conflicting accounts of what happened as the smaller group reconvened.

Sondland has testified that he didn’t know of any Biden connection in Trump’s demands for a Burisma investigation until much later, after the allegations in the whistleblower complaint became known. He has also said that no White House officials ever expressed any concern to him about his efforts to push Ukraine to commit to the Burisma probe. His lawyer declined to comment Tuesday after the release of Vindman’s opening statement.

Sondland’s account is contradicted by statements from Hill and Vindman. Hill testified that she entered the Ward Room as the follow-up meeting was already underway and heard Sondland say the word “Burisma” as he resumed pressing the Ukrainians to pursue certain investigations. She then ordered that meeting to an immediate close.

Vindman said that Sondland used the downstairs meeting to press for “investigations into the 2016 election, the Bidens and Burisma.” Vindman said he then confronted Sondland, saying that “his statements were inappropriate, that the request to investigate Biden and his son had nothing to do with national security, and that such investigations were not something the [National Security Council] was going to get involved in or push.”

Hill then returned upstairs to relay what she had witnessed to Bolton, who exploded, saying, “I am not part of whatever drug deal Sondland and Mulvaney are cooking up.” Mick Mulvaney, the acting White House chief of staff, had met with Sondland on several occasions to discuss Ukraine.

Bolton directed Hill to report what she had witnessed to John Eisenberg, the top lawyer for the National Security Council. Hill spoke briefly with Eisenberg on July 10, but because the attorney was pressed for time they did not finish their discussion until the next day. Hill was accompanied by Wells Griffith, an NSC official responsible for energy policy who is also being sought as a witness by House investigators.

Vindman said that after the Ward Room meeting, he “reported my concerns to the NSC’s lead counsel.”

Despite the heated reactions by Bolton and others to the July 10 meetings, it is not clear whether he, Eisenberg or others took significant steps afterward to intervene and prevent the campaign to pressure Ukraine from proceeding.

Eight days later, at Trump’s direction, Mulvaney ordered the Office of Management and Budget to place a hold on $391 million in security aid to Ukraine meant to help the country fend off Russian aggression.

A week after the aid was held up, Trump spoke with Zelensky by phone, emphasizing U.S. generosity toward Ukraine, complaining about a lack of reciprocation and issuing his request for “a favor though.” Trump proceeded to push Ukraine to investigate Biden, Burisma and the 2016 conspiracy claims he had embraced.

Hill left the White House on July 19, and while she conveyed her concerns about Ukraine to Taylor and others before leaving, she was not in a position to monitor the July 25 call.

Bolton’s actions regarding Ukraine after the July 10 meetings are not clear. Despite his supposed fury about the scheme to pressure Ukraine, Bolton instructed Hill to speak with lawyers rather than doing so himself. It is not clear whether he fought to prevent the aid from being disrupted. And he did not participate in the Trump-Zelensky call.

Because of his high rank and direct involvement in the events surrounding Ukraine, Bolton is regarded as a key witness by impeachment investigators, but he has not yet agreed to testify.

Paul Sonne, Aaron C. Davis and Greg Jaffe contributed to this report.