President Trump pressed the leader of Ukraine to investigate the son of former vice president Joe Biden in a call between the two leaders that is at the center of an extraordinary whistleblower complaint, according to two people familiar with the matter who spoke on the condition of anonymity because of the sensitivity of the matter.

Trump used the July 25 conversation with Ukrainian President Volodymyr Zelensky to pressure the recently elected leader to pursue an investigation that Trump thought would deliver potential political dirt on one of his possible challengers in 2020, the people said.

The descriptions of the call provide the clearest indication to date that Trump sought to use the influence of his office to prod the leader of a country seeking American financial and diplomatic support to provide material that could aid the president’s reelection. After spending much of his presidency fending off allegations that he welcomed 2016 campaign help from Russia, Trump now stands accused of soliciting political ammunition from a country next door to Russia.

Trump on Friday repeated his denial that he has done anything untoward in his conversations with world leaders, but he refused to address whether he had raised the issue of a dormant investigation of a company that previously employed the Democratic presidential contender’s son, Hunter Biden.

“It doesn’t matter what I discussed,” said Trump, who criticized journalists for covering the issue. “It’s another media disaster,” Trump said, even though the intelligence community’s inspector general has assessed the whistleblower complaint as credible and a matter of such urgency that it should be disclosed to the relevant committees in Congress.

One source familiar with the contents of the phone call said that Trump did not raise the issue of American military and intelligence aid that the administration was at the time withholding from Ukraine — indicating that there may not have been an explicit quid pro quo expressed in that conversation.

The call, however, is part of a broader set of facts included in the whistleblower complaint that is at the center of a showdown between the executive branch and Congress, with officials in the Trump administration refusing to divulge information about the substance of an Aug. 12 complaint to the inspector general of the U.S. intelligence community.

Other former U.S. officials familiar with the substance of the whistleblower complaint said it alleges that Trump at some point came closer to conveying a proposed quid pro quo. They said the complaint described a “promise” the president made or an offer of some benefit to a foreign leader.

The revelation that Trump pushed Zelensky to pursue the probe of a company with links to Biden, which was first reported by the Wall Street Journal, helps to explain why a U.S. intelligence official who apparently learned about the call felt compelled to file a whistleblower action against the president.

The disclosure comes amid new details about the White House’s role in preventing acting director of national intelligence Joseph Maguire from complying with congressional demands for the material in the complaint.

White House counsel Pat Cipollone has been engaged in the matter since shortly after the whistleblower action surfaced, officials said, helping to identify legal obstacles to the sharing of information that could be politically damaging to Trump.

Cipollone’s involvement reveals a more direct White House role in the dispute than has previously been reported.

The issue has become a source of tension between the White House and the office of the DNI, with Maguire forced into the position of fending off lawmakers’ demands — citing jurisdictional objections — while the White House avoids asserting executive privilege or taking a clear legal position.

Maguire’s scheduled testimony in open session before the House Intelligence Committee next week could force the White House’s hand. He is almost certain to face questions about any direction he has taken from the White House.

Maguire has turned to the White House and the Justice Department’s Office of Legal Counsel for guidance on the matter, according to a senior administration official who said, “Those consultations are ongoing. At no time has Pat Cipollone personally directed the DNI to withhold information from Congress.”

Cipollone and a White House spokesman declined to comment.

On Capitol Hill, Democratic lawmakers described Trump’s apparent conduct as a grave matter of national security.

“If the President has done what has been alleged, then he is stepping into a dangerous minefield with serious repercussions for his Administration and our democracy,” House Speaker Nancy Pelosi (D-Calif.) said in a statement.

Republicans, however, were instinctively protective of Trump and said they needed to see more information about the whistleblower complaint before making a determination.

“If there’s wrongdoing, certainly we need to look at it,” said Rep. Mark Meadows (R-N.C.), a Trump loyalist. “But my understanding of what has taken place is, this is just a different version of Russia collusion — Russiagate 2.0.”

Biden addressed the issue of his son’s business dealings in Ukraine on Friday after emerging from a campaign event in Cedar Rapids, Iowa. “Wait a second,” Biden said, raising his hands to silence reporters. “Not one single credible outlet has given any credibility to these assertions. Not one single one. And so I have no comment except the president should start to, uh, be president.”

Biden later issued a statement calling for the release of the transcript of Trump’s call with Zelensky and saying, “If these reports are true, then there is truly no bottom to President Trump’s willingness to abuse his power and abase our country. This behavior is particularly abhorrent because it exploits the foreign policy of our country and undermines our national security for political purposes.”

The administration has rebuffed lawmakers’ demands for details about the whistleblower complaint, arguing that the communications and conduct at issue fall outside the intelligence director’s jurisdiction.

But the administration’s position is disputed by the intelligence community’s inspector general, Michael Atkinson, who said in a Sept. 17 letter to Congress that the whistleblower’s allegation not only falls within the DNI’s jurisdiction “but relates to one of the most significant and important of the DNI’s responsibilities to the American people.”

That language appears to be a reference to the intelligence community’s responsibility to defend the country’s ability to protect U.S. elections from foreign interference, a role whose importance has grown dramatically in the aftermath of Russia’s extensive efforts to help Trump win the 2016 election.

Trump has consistently refused to acknowledge Russia’s interference, ignoring the consensus views of U.S. intelligence agencies and one of the core conclusions of the investigation conducted by special counsel Robert S. Mueller III.

Trump’s alleged effort to pressure Zelensky would be all the more remarkable because of the enormous scrutiny the president faced during the first two years of his tenure related to his campaign’s ties to Russia.

Some Democrats said Friday that if Trump sought to orchestrate a quid pro quo with Ukraine, that act would warrant his removal from office.

“This is all impeachable,” Sen. Brian Schatz (D-Hawaii) wrote on Twitter. “Not a close call. We need more facts, but we would be derelict in our duties not to pursue the facts wherever they lead.”

Trump’s call with Zelensky came at a time when the administration appeared to be using aid and access as leverage in its relationship with the Ukrainian leader’s fledgling government.

The United States had pledged $250 million of military and intelligence aid to Ukraine as support for a country that has sought closer ties to the West in the face of aggression and interference from Russia.

The administration withheld that aid until last week when the whistleblower issue erupted in public. Trump had also resisted meeting with Zelensky, for whom an audience with the U.S. president would send a powerful signal to Moscow. But a senior administration official said Friday that Trump would meet Zelensky next week at the United Nations General Assembly in New York.

Trump’s personal lawyer Rudolph W. Giuliani has been unusually active — meeting overseas with Ukrainian officials and working through surrogates — to push government investigators to reopen a probe of a gas company that had hired Hunter Biden to serve as a board member and adviser while his father was U.S. vice president.

In a volatile television appearance on Thursday, Giuliani initially denied that he had demanded that Ukraine dig deeper into the probe involving Biden before reversing himself and admitting he had done so.

On CNN, Giuliani also insisted that there would be nothing improper if Trump applied similar pressure to Zelensky, saying that demanding that a nation receiving U.S. aid crack down on corruption is part of the role of a U.S. president.

Holly Bailey in Cedar Rapids, Iowa, and Philip Rucker, Mike DeBonis, Julie Tate and Shane Harris in Washington contributed to this report.