Rep. Adam Schiff (D-CA) attempted to push former U.S. Special Envoy to Ukraine Kurt Volker to testify during his secret deposition early this month in favor of the allegation that President Donald Trump leveraged aid to Ukraine in exchange for it investigating Joe Biden and his son. The effort failed.

Despite Republican calls for Schiff, the leader of the Democrats’ impeachment probe, to release the transcript of Volker’s deposition behind closed doors, Schiff has refused to do so. Details of Volkers’ October 3 deposition behind closed doors are still pouring out.

On Wednesday, the Washington Examiner reported:

In a secret interview, Rep. Adam Schiff, leader of the House Democratic effort to impeach President Trump, pressed former United States special representative to Ukraine Kurt Volker to testify that Ukrainian officials felt pressured to investigate former Vice President Joe Biden’s son Hunter as a result of Trump withholding U.S. military aid to Ukraine. Volker denied that was the case, noting that Ukrainian leaders did not even know the aid was being withheld and that they believed their relationship with the U.S. was moving along satisfactorily, without them having done anything Trump mentioned in his notorious July 25 phone conversation with Ukrainian President Volodymyr Zelensky. When Volker repeatedly declined to agree to Schiff’s characterization of events, Schiff said, “Ambassador, you’re making this much more complicated than it has to be.”

Volker also testified that Ukrainian officials did not express concerns about being pressured to investigate the Bidens in exchange for aid.

The former envoy reportedly also noted that there was no quid pro quo, as claimed by House Democrats pursuing the impeachment probe.

Ukraine did not learn the U.S. was withholding aid until a story appeared in the press in late August, well after the infamous July 25 call.

A “whistleblower’s” claim that Trump pressured Ukrainian President Volodymyr Zelensky to investigate Joe Biden and his son, Hunter, in exchange for aid during a July 25 call is at the heart of the probe.

The “whistleblower” alleged Trump made Zelensky a quid pro quo offer — U.S. aid in exchange for investigating former Vice Presiden Biden and his son. Trump and Zelennsky have denied the allegation.

Citing Ukraine’s acting foreign minister at the time of the July 25 call, BuzzFeed acknowledged that the country was not aware that the U.S. was withholding the aid until late August

“I don’t believe the Ukrainians were aware that the assistance was being held up,” Volker told Schiff on October 3, according to the Examiner, later adding, “They became aware later, but I don’t believe they were aware at the time, so there was no leverage implied.”

Volker made a surprise return to the Capitol on Wednesday to review his testimony.

“I was never asked to do anything that I thought was wrong, including by the [U.S.] president,” Volker stressed behind closed doors on Wednesday, CBS News learned from unnamed sources.

On October 3, he testified that the Trump administration was not trying to coerce Ukraine to investigate Biden in exchange for aid.

Schiff has vowed to release all the transcripts of the testimony provided by impeachment probe witnesses but refuses to say when. So far, House Democrats have conducted all depositions in private.