House Democrats leading the impeachment investigation into President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE are asking acting White House chief of staff Mick Mulvaney Mick MulvaneyOn The Money: House panel pulls Powell into partisan battles | New York considers hiking taxes on the rich | Treasury: Trump's payroll tax deferral won't hurt Social Security Blockchain trade group names Mick Mulvaney to board Mick Mulvaney to start hedge fund MORE to testify Friday.

“Based on evidence gathered in the impeachment inquiry and public reporting, we believe that you possess substantial first-hand knowledge and information relevant to the House’s impeachment inquiry,” House Intelligence Chairman Adam Schiff Adam Bennett SchiffSchiff to subpoena top DHS official, alleges whistleblower deposition is being stonewalled Schiff claims DHS is blocking whistleblower's access to records before testimony GOP lawmakers distance themselves from Trump comments on transfer of power MORE (D-Calif.), House Foreign Affairs Chairman Eliot Engel Eliot Lance EngelHouse panel halts contempt proceedings against Pompeo after documents turned over Engel subpoenas US global media chief Michael Pack The Hill's Morning Report - Sponsored by The Air Line Pilots Association - Pence lauds Harris as 'experienced debater'; Trump, Biden diverge over debate prep MORE (D-N.Y.) and acting House Oversight Chairwoman Carolyn Maloney Carolyn Bosher MaloneyPelosi, Democrats unveil bills to rein in alleged White House abuses of power Government watchdog recommends creation of White House cyber director position Top Democrats call for DOJ watchdog to probe Barr over possible 2020 election influence MORE (D-N.Y.) said in a joint letter sent to Mulvaney on Tuesday.

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The Democrats said information revealed earlier in the impeachment inquiry shows Mulvaney played a "direct role" in Trump's alleged solicitation of foreign interference in the 2020 election.

They also said evidence gathered during depositions suggests Mulvaney “may have coordinated” with U.S. Ambassador to the European Union Gordon Sondland, the president’s personal attorney Rudy Giuliani Rudy GiulianiThe Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting CIA found Putin 'probably directing' campaign against Biden: report Democrats fear Russia interference could spoil bid to retake Senate MORE and others to “carry out President Trump’s scheme” in “pursuit of investigations” into former Vice President Joe Biden Joe BidenFormer Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick Bloomberg rolls out M ad buy to boost Biden in Florida MORE, a 2020 candidate.

Trump’s interactions with Ukraine and are at the center of the impeachment inquiry.

The Democrats also referenced Mulvaney’s Oct. 17 press briefing, where he said the president had held up security aid to Ukraine partly to pressure the country to investigate a conspiracy theory undermining the conclusion that Russia interfered in the 2016 election.

Mulvaney walked those comments back, accusing the media of mischaracterizing his remarks, but Democrats wrote in the letter that Mulvaney “admitted publicly” that Trump ordered to withhold foreign aid for Ukraine to further Trump’s “own personal, political interests, rather than the national interest.”

“Despite your subsequent attempts to walk-back this clear admission, your statements to the American public on Oct. 17 were nothing less than a televised confession that President Trump’s order to freeze Ukraine security assistance was explicitly linked to Ukraine pursuing investigations as part of an effort to bolster the President's 2020 reelection campaign,” Democrats wrote.

White House spokesman Hogan Gidley said the Trump administration will not allow Mulvaney to testify.

“Past Democrat and Republican Administrations would not be inclined to permit Senior Advisers to the President to participate in such a ridiculous, partisan, illegitimate proceeding – and neither is this one,” Gidley said in a statement.

Multiple Trump administration officials scheduled to testify Monday and Tuesday did not show up for their closed-door depositions.

Updated at 5:12 p.m.