Rudy Giuliani was not the only attorney trying to get damaging information on Joe Biden from Ukrainian officials, and President Trump’s decision to withhold aid from Ukraine this summer was made in spite of several federal agencies supporting the aid, Fox News’ Chris Wallace revealed on "Fox News Sunday."

In addition to Giuliani, Washington, D.C., lawyers Joe DiGenova and his wife, Victoria Toensing, worked alongside the former New York City mayor. According to a top U.S. official, the three attorneys were working "off the books" -- not within the Trump administration -- and only the president knows the details of their work.

REPUBLICANS WANT WHISTLEBLOWER’S SOURCES, AS INCONSISTENCIES IN COMPLAINT EMERGE

DiGenova and Toensing have been staunch supporters of President Trump, and were close to joining his legal team during Robert Mueller’s Russia investigation. That ultimately did not happen due to conflicts, as Toensing had previously represented witnesses who had already spoken to Mueller’s team.

In a tweet on Sunday, Toensing denied that her husband and she were working with Giuliani and called the reporting "categorically false." Wallace later responded, "We stand by our story."

When asked by the Fox Business Network's Maria Bartiromo if he was working with other attorneys to get information about Biden, Giuliani denied it.

"No. I didn't work with anybody to try and get dirt on Joe Biden," Giuliani said on "Sunday Morning Futures," claiming that the information was handed to him rather than sought out.

A whistleblower complaint citing "multiple U.S. government officials" accused Trump of pressuring Ukraine to investigate Biden in a July 25 phone call. Democrats have claimed Trump used military aid as leverage over Ukrainian President Volodymyr Zelensky, although Zelensky insisted there was no pressure at all.

Trump claimed that while he did delay aid to Ukraine, it was because he was pushing for European nations such as Germany to provide additional aid to Ukraine, and that he eventually did provide the aid.

Fox News has learned that the Pentagon, State Department and National Security Council were “unanimous” in supporting the aid to Ukraine, and that Trump acted alone in withholding the aid over the summer.

Giuliani has gone on record saying that his investigation began as a probe of possible Ukrainian collusion with the Democratic Party in the 2016 election, which led to him looking into Biden as well. In his call with Zelensky, Trump did reference Crowdstrike, a cybersecurity firm that had worked on an investigation of a hacked Democratic National Committee server. Trump also claimed that the server itself, which the FBI never acquired, may currently be in Ukraine.

The former New York City mayor asserts that Hunter Biden engaged in improper activity related to his business dealings with energy company Burisma Holdings, and claims that then-Vice President Joe Biden used his office to pressure the Ukrainian government into firing top prosecutor Viktor Shokin, who was investigating Burisma.

Biden has acknowledged this in the past, stating that he threatened to withhold $1 billion from Ukraine if they did not fire Shokin. Biden denied wrongdoing, and has not stated that he did this to protect his son, as Shokin had been accused of corruption.

DiGenova and Toensing have called out Biden publicly, accusing him of acting on behalf of his son, and disputing claims that Shokin was corrupt.

INTEL CHIEF DEFENDS HANDLING OF TRUMP CALL COMPLAINT, SPARS WITH SCHIFF IN TENSE HEARING

A memo released by the White House containing the substance of the call showed that the two leaders discussed U.S. aid to Ukraine as well as the Biden investigation. There was no overt link or reference to a quid pro quo, but Democrats claim the pressure was implied.

Speculation that Trump may have sought campaign assistance from a foreign government -- and the allegation that he used military aid as leverage – has increased demand from Democrats that Trump be impeached, where the party had been split on the issue in the past. While figures such as House Judiciary Committee Chairman Jerrold Nadler, D-N.Y., have long touted efforts to investigate Trump for the purpose of impeachment, House Speaker Nancy Pelosi had been hesitant to support such a move, out of fear that the move would be politically divisive if the American people did not support it.

After news of the whistleblower complaint came out, however, Pelosi called for a formal impeachment inquiry.

Republicans, meanwhile are criticizing the complaint because the whistleblower did not have firsthand knowledge of the call. Top Republicans have been pushing for the identity the whistleblower’s government sources.

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Republicans specifically questioned why the whistleblower's sources in the White House didn't file a complaint themselves -- especially given that relevant whistleblower procedures did not protect second-hand complaints until just days before the whistleblower filed the complaint against Trump. (The New York Times reported that the whistleblower is a CIA officer detailed to the White House. Fox News has not confirmed The Times' report.)

Rep. Andy Biggs, R-Ariz., a member of the House Judiciary Committee, told Fox News' "Shepard Smith Reporting" on Thursday that the administration had an apparent "leak problem," adding, "if they're leaking something that's supposed to be classified, then ... that probably is criminal in nature."

Fox News’ Gregg Re, John Roberts, Brooke Singman and Fox Business Network's Maria Bartiromo contributed to this report.