WASHINGTON — Speaker Nancy Pelosi sharpened the focus of Democrats’ impeachment case against President Trump on Thursday, accusing the president of committing bribery when he withheld vital military assistance from Ukraine at the same time he was seeking its commitment to publicly investigate his political rivals.
The speaker’s explicit allegation of bribery, a misdeed identified in the Constitution as an impeachable offense, was significant. Even as Ms. Pelosi said that no final decision had been made on whether to impeach Mr. Trump, it suggested that Democrats were moving toward a more specific set of charges that could be codified in articles of impeachment in the coming weeks. It also indicated that Democrats were working to put a simple name to the president’s alleged wrongdoing that would resonate with the public.
“The devastating testimony corroborated evidence of bribery uncovered in the inquiry, and that the president abused his 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 — a clear attempt by the president to give himself an advantage in the 2020 election,” Ms. Pelosi told reporters at her weekly news conference in the Capitol.
The remarks came as impeachment investigators closed in on two potentially significant breakthroughs that could help build their case.
A second witness emerged to corroborate a key episode revealed during public impeachment testimony on Wednesday that further tied Mr. Trump to the pressure campaign on Ukraine. The account of a telephone call in which the president discussed his interest in having Ukraine begin investigations will help bolster Democrats’ case against Mr. Trump, but it could also undercut the credibility of their best witness who can describe direct conversations with the president.
Later Thursday, a high-ranking career official appeared poised to become the first witness to cooperate with the inquiry from the White House Office of Management and Budget, which played a key role in holding up the delivery of $391 million in security assistance at the center of the inquiry. A lawyer for the official, Mark Sandy, said that he would appear for a deposition on Saturday if subpoenaed, despite orders from the White House not to.
Mr. Trump worked to defend himself and shore up his support among Republicans who could decide the fate of his presidency. Over lunch at the White House, he showed a group of Republican senators a reconstructed transcript of a congratulatory phone conversation he had in April with President Volodymyr Zelensky of Ukraine. Mr. Trump has promised repeatedly to release the document, in part to counter the notion that he ever pressured Mr. Zelensky, but by Thursday evening it had not been made public.
“He just shuffled it across the table,” Senator Kevin Cramer of North Dakota, who attended the lunch, told reporters afterward, calling the conversation “a very nice, congratulatory call.”
“It said ‘Congratulations, you ran a great campaign.’ ‘Oh, thank you, Mr. President, look forward to working with you,’” Mr. Cramer said.
The president’s thinking seemed to be that the congratulatory April call might draw attention away from his July exchange with Mr. Zelensky in which he pressed the Ukrainian president to investigate former Vice President Joseph R. Biden Jr. and a discredited theory about Democrats conspiring with Ukraine to interfere in the 2016 election. Democrats consider a reconstructed transcript of that call their most damning evidence against Mr. Trump.
The House Intelligence Committee plans to convene another impeachment hearing on Friday, calling Marie L. Yovanovitch, the former American ambassador to Ukraine whose ouster by Mr. Trump, some members say, set the stage for his pressure campaign.
The Intelligence Committee convened the House’s first public impeachment hearing in two decades on Wednesday with testimony from William B. Taylor Jr., the top American diplomat in Ukraine, and George P. Kent, a senior State Department official responsible for policy toward the country.
They told the committee that Mr. Trump and his allies inside and outside the government placed the president’s political objectives at the center of American policy toward Ukraine, using as leverage both the security assistance that Congress had appropriated for Ukraine’s war with Russia as well as a White House meeting that was coveted by the country’s new leader.
The new witness who emerged on Thursday, Suriya Jayanti, a State Department official in Kiev, would be able to describe a phone call she overheard between the president and Gordon D. Sondland, the United States ambassador to the European Union, in which they discussed the investigations Mr. Trump sought. Ms. Jayanti sat at a restaurant with Mr. Sondland and at least one other embassy official, David Holmes, as Mr. Sondland and Mr. Trump spoke by phone in July, according to two people briefed on the matter.
During that call, Mr. Trump brought up the investigations he sought and Mr. Sondland said the Ukrainians were prepared to move forward with them. After the call, Mr. Sondland told at least Mr. Holmes that Mr. Trump cared more about the investigations his personal lawyer Rudolph W. Giuliani had been pushing the Ukranians to commit to than about Ukraine.
The conversation took place just a day after the July 25 in which Mr. Trump raised the investigations with Mr. Zelensky.
Mr. Taylor first disclosed the existence of the call during his testimony on Wednesday. Investigators plan to interview Mr. Holmes privately on Friday to press for additional details. They may also ask Ms. Jayanti to testify.
Though her account bolsters Democrats’ accusations, it raises new questions about the credibility of Mr. Sondland, who is scheduled to testify publicly next week. Because the White House has blocked other officials from cooperating, Mr. Sondland is one of the few witnesses who spoke directly with Mr. Trump and is therefore important to Democrats’ case. But he already substantially revised his testimony once, admitting that he told a top Ukrainian official in September that the country would probably not receive military aid unless it announced the investigations that Mr. Trump wanted.
Now it has become clear that he also failed to disclose to the committee the July call he had with Mr. Trump.
Republicans pounced on the inconsistencies to try to discredit Mr. Sondland, a wealthy hotelier and Trump campaign donor who had no diplomatic experience before the president installed him as an ambassador.
“I think that if Ambassador Sondland’s credibility is questioned, it makes it really hard for the Democrats to impeach, because everything is based on Ambassador Sondland,” said Representative Mark Meadows, Republican of North Carolina.
Democrats have not exactly been forgiving, either, but they argue that Republicans are overstating the implications for the case they are building, particularly if Mr. Sondland confirms the new details.
“Obviously it doesn’t help his credibility,” said Representative Sean Patrick Maloney, Democrat of New York. “But no one can dispute he is a person with important information who was at the center of these events, a firsthand witness to the president’s actions. All we want from Ambassador Sondland is the whole truth, and nothing but.”
Rank-and-file Democrats have begun using the term “bribery” more freely in recent days to describe what a string of diplomats and career Trump administration officials have said was a highly unusual and inappropriate effort by Mr. Trump and a small group around him to extract a public promise from Ukraine for investigations.
But Ms. Pelosi’s remarks on impeachment were the first time she discussed the growing inquiry at length with reporters since Congress recessed in late October.
“The bribe is to grant or withhold military assistance in return for a public statement of a fake investigation into the elections,” Ms. Pelosi said, clarifying her choice of words. “That’s bribery.”
Ms. Pelosi was referring to Article II of the Constitution, which states that the president and other public officers “shall be removed from office on impeachment for, and conviction of, treason, bribery, or other high crimes and misdemeanors.” The founders, who were preoccupied with the young republic’s independence from foreign influence, included the term to ensure the president was acting in the interest of the United States.
“The framers had this concept of an illicit exchange, the president using his power in exchange for something that was beneficial for him, and perhaps vice versa,” said Michael J. Gerhardt, a constitutional law professor and an impeachment scholar at the University of North Carolina.
For Democrats, the term may also help solve a communications challenge. After weeks of describing the president’s actions as a “quid pro quo,” lawmakers are looking for a more straightforward and digestible way to describe what happened to their constituents.
“English words are easier to understand than Latin words,” said Representative Jim Himes, Democrat of Connecticut.
Asked if Democrats were successfully bringing the public along with them, Ms. Pelosi conceded that the country was likely too polarized to ever support impeachment as overwhelmingly as it did when President Richard M. Nixon resigned in 1974. Public opinion polls now suggest a majority of Americans favor the impeachment inquiry, but only by a thin margin.
“Impeaching is a divisive thing in our country — it’s hard,” Ms. Pelosi said. “The place that our country is now, it’s not a time where you’ll go to 70 percent when President Nixon walked out of the White House.”
Indeed, there was no sign from congressional Republicans that the testimony had shaken their conviction that Mr. Trump is innocent.
Representative Kevin McCarthy, Republican of California and the minority leader, told reporters that the hearing had only confirmed that the accounts from Mr. Taylor, Mr. Kent and other witnesses who have offered damaging information about Mr. Trump are not firsthand, and therefore could not be trusted. And he pointed to the July phone call between Mr. Trump and Mr. Zelensky that is at the heart of the impeachment inquiry as exculpatory, despite Democrats’ claims to the contrary.
“The call summary is still the most important piece of evidence we have, and it shows no pressure or even mention of conditionality between the two leaders,” Mr. McCarthy said.
In an interview, he added that he did not put much stock in Ms. Pelosi’s use of the term “bribery” either.
“Wait ’til tomorrow ’til she makes a new term, because every term she brings forward, there’s no proof behind it,” he said.
Julian E. Barnes and Emily Cochrane contributed reporting.