Hours after Acting White House Chief of Staff Mick Mulvaney claimed "absolute immunity" from cooperating with the House impeachment probe into President Donald Trump, Democrats leading the inquiry released sworn testimony from two key witnesses who placed the chief of staff at the center of President Donald Trump's effort to pressure Ukraine to investigate Joe Biden.

Fiona Hill, Trump's former top Russia adviser, told House impeachment investigators last month about a July 10 meeting in which U.S. Ambassador to the European Union Gordon Sondland "blurted out" Mulvaney's role in arranging a White House visit for Ukrainian President Volodymyr Zelensky.

"Mulvaney personally ordered the hold on Ukraine aid. His refusal to come forward and tell Congress why he did that is utterly damning."

—Rep. Don Beyer (D-Va.)

"Well, we have an agreement with the chief of staff for a meeting if these investigations in the energy sector start," Sondland said, according to Hill. Sondland was apparently referring to Burisma, a natural gas company that used to employ Hunter Biden, the former vice president's son.

Then-national security adviser John Bolton "immediately stiffened and ended the meeting" after Sondland's remarks, Hill told House Committees.

Lt. Col. Alexander Vindman, a National Security Council official who listened to Trump's July 25 phone call with Zelensky, corroborated Hill's account of the White House meeting, which was attended by Ukrainian officials and Trump advisers.

"Sondland relatively quickly went into outlining how the—you know, these investigations need to—on the deliverable for these investigations in order to secure this meeting [between Trump and Zelensky]," Vindman said. "I heard him say that this had been coordinated with White House Chief of Staff Mr. Mick Mulvaney."

Erin Banco, national security reporter for The Daily Beast, reported that Hill and Vindman's testimonies "mark the most direct link between the scandal now imperiling the presidency and the president's chief of staff."

The depositions were made public just hours after Mulvaney refused to comply with a subpoena to testify as part of House Democrats' impeachment probe.

The acting chief of staff reportedly informed House committees "one minute before" his deposition was scheduled to begin that he would not show up and asserted "absolute immunity."

Legal analysts on Friday swiftly called into question the legal basis for Mulvaney's "absolute immunity claim":

“Absolute immunity”?! What LEGAL fresh hell is this?? *There is no law that says that absolute immunity is conferred to Presidential advisers to block them from appearing pursuant to a Congressional subpoena.* https://t.co/rQHFtOcveE — Katie Phang (@KatiePhang) November 8, 2019 Ooooooh we’ve moved from executive privilege to “absolute immunity.” Fantasy Law looks fun, maybe I’ll teach it next semester https://t.co/WBVf90Rn1a — Asha Rangappa (@AshaRangappa_) November 8, 2019

Mulvaney, who previously ran the Office of Management and Budget, became a focus of House Democrats' investigation after the Washington Post reported in September that he put a hold on $400 million of appropriated Ukraine aid on instructions from Trump. During a press briefing last month, Mulvaney admitted the aid was withheld to pressure Ukraine to launch investigations on behalf of Trump.

Rep. Don Beyer (D-Va.) tweeted Friday that it is "hard to imagine something more suspicious and damaging than the White House's own chief of staff afraid to tell the truth under oath."

"Mulvaney personally ordered the hold on Ukraine aid," said Beyer. "His refusal to come forward and tell Congress why he did that is utterly damning."