Democrats sharpened their case for impeachment Thursday, escalating their rhetoric against President Trump as additional evidence emerged potentially implicating him directly in the abuse-of-power controversy surrounding U.S. relations with Ukraine.

Using her most aggressive language yet, House Speaker Nancy Pelosi (D-Calif.) accused Trump of committing “bribery” by seeking to use U.S. military aid as leverage to pressure the Ukrainian government to conduct investigations that could politically benefit the president.

Pelosi’s move to cite a specific constitutional offense and move away from using the lawyerly Latin term “quid pro quo” to describe the president’s actions came as a second official from the U.S. Embassy in Kyiv was revealed to have overheard Trump discussing political “investigations” in a July 26 phone call with Gordon Sondland, the U.S. ambassador to the European Union who served as a key liaison between the White House and Ukraine’s fledgling government.

That phone call, which Trump has said he doesn’t recall, is expected to play a pivotal role in upcoming impeachment proceedings, as Democrats seek to directly tie Trump to what they charge was a bribery scheme worthy of removal from office. David Holmes, an embassy staffer in Ukraine who allegedly overheard Trump discussing “investigations” with Sondland, is slated to testify behind closed doors in the House impeachment probe Friday.

Democrats have seized on Holmes’s allegation — which was revealed Wednesday during testimony by William B. Taylor Jr., the acting U.S. ambassador to Ukraine — as evidence of Trump’s culpability in impeachable offenses.

Pelosi said Thursday that testimony by Taylor and Deputy Assistant Secretary of State George Kent highlighted how Trump had abused his power. Both senior diplomats testified that it was inappropriate for Trump and his allies to push for investigations targeting former vice president Joe Biden, a 2020 presidential candidate, and a debunked theory about Ukrainian interference in the 2016 election.

“The devastating testimony corroborated evidence of bribery uncovered in the inquiry and that the president abused power and violated his oath by threatening to withhold military aid and a White House meeting in exchange for an investigation into his political rival,” Pelosi said at her weekly news conference.

In response, the White House and congressional Republicans have emphasized the diplomats’ lack of firsthand knowledge of Trump’s actions on Ukraine.

GOP lawmakers argued that Kent and Taylor have never spoken directly to Trump — and therefore cannot say with confidence that he tried to strong-arm a U.S. ally into doing him political favors.

“Their understanding, which is the foundation of the case for the Democrats, was based on secondhand information,” House Minority Leader Kevin McCarthy (R-Calif.) told reporters Thursday.

For his part, Trump continued to complain about the impeachment proceedings.

“This Impeachment Hoax is such a bad precedent and sooo bad for our Country!” he wrote on Twitter.

On Friday, the impeachment hearings will continue with public and private testimony.

Marie Yovanovitch, the former ambassador to Ukraine who was recalled earlier this year by Trump, is scheduled to appear at an open hearing of the House Intelligence Committee.

Yovanovitch said in an Oct. 11 deposition that she was the target of a smear campaign to orchestrate her removal that involved Trump’s personal attorney Rudolph W. Giuliani and Ukrainian officials suspected of fostering corruption, according to a transcript.

While Yovanovitch’s testimony could help Democrats build a broad case that Trump and Giuliani were using conspiracy theories and shadowy arrangements to advance their personal and political interests in Ukraine, Holmes’s private testimony is expected to be more critical to the central thrust of the impeachment inquiry.

In his testimony Wednesday, Taylor quoted the embassy staffer saying that after he overheard Trump inquire about “the investigations” on a phone call with Sondland, he heard Sondland tell the president “that the Ukrainians were ready to move forward.” The aide also said Sondland later described Trump as more interested in “the investigations of Biden, which Giuliani was pressing,” than Ukraine policy, Taylor testified. Taylor did not name the staff member, but several people familiar with the situation have confirmed it was Holmes.

Suriya Jayanti, a Foreign Service officer based at the U.S. Embassy in Kyiv, also overheard the phone call that was described by Taylor, according to a person familiar with the matter, who spoke on the condition of anonymity Thursday to discuss a matter involved in the impeachment proceedings. It’s not clear if Democrats will seek testimony from Jayanti.

The July 26 call came a day after Trump pushed for investigations into Biden and a debunked conspiracy theory about Ukrainian election meddling during a conversation with Ukrainian President Volodymyr Zelensky.

While Republicans have struggled to rally around a consistent defense of Trump in the face of weeks of incriminating revelations, on Thursday they sought to undermine the witness testimony by dismissing it as “hearsay.”

Rep. Douglas A. Collins (R-Ga.), who is not a member of the House Intelligence Committee, took to Twitter during the hearing for a bit of amplification. He posted a scene from the 1986 movie “Ferris Bueller’s Day Off” in which a character explains the protagonist’s absence from class: “My best friend’s sister’s boyfriend’s brother’s girlfriend heard from this guy who knows this kid who’s going with the girl who saw Ferris pass out at 31 Flavors last night.”

“A live look into Ambassador Taylor’s testimony in the Schiff impeachment proceedings,” Collins wrote.

The strategy, however, could be risky. Witnesses with firsthand knowledge of some of the president’s actions are set to testify publicly next week, including Sondland, and others are currently being blocked by the White House.

One longtime career employee at the White House Office of Management and Budget is expected to break ranks and testify behind closed doors Saturday, potentially filling in important details on the holdup of military aid to Ukraine. Mark Sandy would be the first OMB employee to testify in the inquiry, after OMB acting director Russell T. Vought and two other political appointees at the agency defied congressional subpoenas to appear.

But unlike these other OMB officials, Sandy is a career employee, not one appointed by the president. He has worked at the agency off and on for over a decade, under presidents of both parties, climbing the ranks to his current role as deputy associate director for national security programs.

Sandy could provide insight into the process by which Trump’s White House held up $400 million in military and security aid to Ukraine over the summer. So far, none of Trump’s defenders have provided a clear explanation for why the aid was frozen, only to be released after a whistleblower came forward with a report that was flagged to Congress.

In a message to Trump and in response to the GOP criticism, Pelosi said, “If the president has something that is exculpatory — Mr. President, that means you have anything that shows your innocence — then he should make that known.”

Pelosi’s embrace of the term bribery — one of only two crimes specifically cited in the Constitution as impeachable — comes after nearly two months of debate over whether Trump’s conduct amounted to a “quid pro quo” — a Latin term describing an exchange of things of value.

Bribery, Pelosi suggested, amounted to a translation of quid pro quo that would stand to be more accessible to Americans: “Talking Latin around here: E pluribus unum — from many, one. Quid pro quo — bribery. And that is in the Constitution, attached to the impeachment proceedings.”

Article II of the Constitution holds that the president and other civil federal officials “shall be removed from Office on Impeachment for, and Conviction of, Treason, Bribery, or other high Crimes and Misdemeanors.”

Several Democrats have stopped using the term “quid pro quo,” instead describing “bribery” as a more direct summation of Trump’s alleged conduct.

The shift came after the Democratic Congressional Campaign Committee conducted focus groups in key House battlegrounds in recent weeks, testing messages related to impeachment. Among the questions put to participants was whether “quid pro quo,” “extortion” or “bribery” was a more compelling description of Trump’s conduct. According to two people familiar with the results, which circulated among Democrats this week, the focus groups found “bribery” to be most damning. The people spoke on the condition of anonymity because the results have not been made public.

Rep. Jim Himes (D-Conn.), a House Intelligence Committee member, kicked off the effort to retire “quid pro quo” from the Democratic vocabulary during a Sunday appearance on NBC’s “Meet the Press,” where he said “it’s probably best not to use Latin words” to explain Trump’s actions.

On Thursday, he told reporters that “bribery” was a useful, if not altogether precise way to summarize the allegations.

“Abuse of power is not necessarily a concept that most Americans run around thinking about,” he said. “In this case, the abuse of power was some combination of bribery and extortion.”

GOP lawmakers said the shift in messaging would do little to change public perception of the impeachment effort.

“They’re trying a different narrative to see if that works,” said Rep. Brad Wenstrup (R-Ohio), a House Intelligence Committee member. “ ‘Quid pro quo’ was squashed. If it wasn’t, they would still be saying it, right? And, so, now they’ll try a different term.”

Sondland, however, told lawmakers that he never talked to Trump about leveraging military aid and a head-of-state meeting with Ukraine on a promise to investigate the Bidens, a major discrepancy he will be pushed to clear up next week.

Both parties are seeking to sharpen their messaging ahead of critical testimony next week, including an open hearing Wednesday featuring Sondland. The Trump donor and diplomat has previously amended his private testimony to confirm that he told Ukrainian officials that they needed to announce political investigations to obtain frozen military assistance and a meeting with Trump.

Sondland told at least four Trump officials that the president personally oversaw the entire operation, and his alleged July 26 phone call with the president could become a key piece of incriminating evidence establishing Trump’s personal interest in orchestrating Ukrainian investigations into Biden and his son, Hunter.

Paul Sonne, Erica Werner, John Wagner, Rachael Bade and Josh Dawsey contributed to this report.