At least one National Security Council official alerted the White House's national security lawyers about the concerns, three sources familiar with the matter said, a detail that had not been previously disclosed. Those same lawyers would later order the transcript of the call moved to a highly classified server typically reserved for code-word classified material.
Those concerns were raised independently of the complaint brought forward by an intelligence community whistleblower. They reflect new evidence of the unease mounting within the administration at the President's actions.
Unsettled aides also immediately began quizzing each other about whether they should alert senior officials who were not on the call -- mainly those at the Justice Department, since Trump had invoked the agency's boss, Attorney General Bill Barr, multiple times during the 30-minute talk.
White House lawyers, aware of the tumult, initially believed it could be contained within the walls of the White House. As more people became aware of the conversation -- and began raising their internal concerns about it -- a rough transcript of the call was stored away in a highly classified server that few could access.
The order to move the transcript came from the White House's national security lawyers to prevent more people from seeing it, according to people familiar with the situation. It also came after recognition the document would need to be preserved for legal reasons.
As the level of worry mounted, however, it would become clear the issue could not be contained to the executive branch. Two whistleblowers have come forward to allege Trump improperly used his position to pressure Ukraine into investigating Biden. That's led Democrats to open an impeachment inquiry into Trump and spurred allegations he abused his power for political gain.
The concerns and complaints that White House lawyers once believed would be contained to the executive branch have put the presidency in crisis.
Before all that, the call, which began just past 9 a.m. ET, wasn't viewed by many of Trump's foreign policy aides as a highly sensitive conversation, unlike some of his other phone calls with international counterparts.
Instead, it was viewed as a customary conversation -- and the result of a longtime effort by aides such as then-national security adviser John Bolton and Energy Secretary Rick Perry to convince Trump to engage the new Ukrainian leader as a counterweight to Russia.
Still, one former White House official said there was a unique sense of anticipation surrounding the conversation stemming partly from Trump's apparent interest in it, something he'd shown few times ahead of previous calls with foreign leaders.
"It was weird," the former official said. "He seemed to be taking interest in this particular country."
Though multiple officials have insisted they were largely out of the loop on concerns over the call, most who work closely with the President were aware of his obsession with Hunter Biden's business dealings in the country. He had been mentioning it more often privately, though several said they didn't realize how much it would escalate or that Trump would raise it directly with his Ukrainian counterpart.
Like most of his phone calls that occur before noon, Trump conducted the conversation from the third-floor White House residence, where he spends most mornings watching television and consulting advisers by phone.
Sitting in his private quarters, Trump wasn't surrounded by the usual clutch of aides who would accompany him in person during a call with a foreign leader made from the Oval Office. Instead, a number of aides were listening in the Situation Room or on their own lines.
Those who listened included Secretary of State Mike Pompeo, who insisted to reporters last week that Trump's conversation was consistent with US policy toward Ukraine.
Tim Morrison, the National Security Council's senior director for Europe and Russia, was on the line. So was Rob Blair, a national security aide to acting chief of staff Mick Mulvaney, and Keith Kellogg, the national security adviser to Vice President Mike Pence. Officials said standard operating procedure suggests Alexander Vindman, the National Security Council's Ukraine expert, would also have been listening in.
Bolton was not on the line. By late July, the relationship between Trump and Bolton was deeply strained. But typically, a national security adviser accompanies the president on phone calls with foreign leaders.
Elsewhere, a State Department interpreter fluent in Ukrainian was providing real-time translation. And a duty officer from the Situation Room took notes that would later be paired with a log of the call using voice recognition software to put together a rough transcript.
Almost as soon as Trump had hung up, word of what he said on the call began to circulate among National Security Council staffers -- in particular, his request that Zelensky investigate Biden. The entreaty caused concern among some of his national security officials, who discussed among themselves whether Trump had crossed a line.
Eventually, the internal consternation escalated. Within roughly a week, the top lawyer at an intelligence agency had contacted John Eisenberg, the top lawyer on the National Security Council, to discuss concerns raised by an intelligence officer through a colleague about a phone call Trump had held with a foreign leader, though didn't specify the country in question.
Eisenberg said he had a vague understanding of the concerns surrounding the Zelensky call and would do some more digging on it, according to person familiar with the matter.
Around the same time, a transcript of the call was being finalized by staffers at the National Security Council. Initially, the process of transcribing and archiving the call followed the standard procedure for dozens of previous presidential calls with foreign leaders: The raw transcript of the call was circulated to a small group of officials, including the national security adviser, deputy national security adviser, members of the National Security Council's executive secretariat and NSC lawyers.
From there, the National Security Council director responsible for Ukraine -- Vindman -- reviewed the document for accuracy before the document made its way to Bolton and his deputy Charlie Kupperman. At that point, the document would ordinarily have been marked "limited access" and shared on a need-to-know basis.
But within a few days, a National Security Council lawyer -- acting on orders from Eisenberg, his boss -- directed council officials to move the transcript to the code-word classified system, a former White House official said, even though there was no code-word classified material discussed during the call.
One person familiar with the matter said it was possible Eisenberg ordered the call transcript placed into the codeword system after his initial call with the CIA's top lawyer to "preserve" the record since he realized it could become a matter of a legal issue. But others familiar with the matter said the move came after officials became aware of the internal concerns and wanted to prevent additional people from reading the document.
White House lawyers initially believed the contents of the complaint would remain within the executive branch and not reach Congress or the public. Several sources said the White House counsel's office kept a very close hold on the initial general counsel disclosure and the ultimate whistleblower complaint until just a few days before the complaint's public release, when it became clear it would reach lawmakers.
Those kept in the dark about those items until the days before their release included Mulvaney and the President's communications aides.
And there is little sign, at least in the call's immediate aftermath, that the President himself was aware of the scramble ensuing among his underlings to contain the fallout of his conversation. An hour-and-a-half after the call ended, Trump departed the White House alongside his son Eric for an event at the Pentagon, leaving the chaos behind.