Aides to House Judiciary Committee Chairman Jerrold Nadler Jerrold (Jerry) Lewis NadlerDemocrats shoot down talk of expanding Supreme Court Schumer: 'Nothing is off the table' if GOP moves forward with Ginsburg replacement Top Democrats call for DOJ watchdog to probe Barr over possible 2020 election influence MORE (D-N.Y.) say the congressman has privately voiced support for impeachment proceedings against President Trump Donald John TrumpSteele Dossier sub-source was subject of FBI counterintelligence probe Pelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Trump 'no longer angry' at Romney because of Supreme Court stance MORE, The Washington Post reported Sunday.

Nadler has not publicly come forward with supporting impeachment inquiries into Trump, despite mounting pressure from within his own party.

On "Fox News Sunday," Nadler said he believes former special counsel Robert Mueller Robert (Bob) MuellerCNN's Toobin warns McCabe is in 'perilous condition' with emboldened Trump CNN anchor rips Trump over Stone while evoking Clinton-Lynch tarmac meeting The Hill's 12:30 Report: New Hampshire fallout MORE's report "presents very substantial evidence that the president is guilty of high crimes and misdemeanors."

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"The administration must be held accountable," he said.

Nadler, however, stopped short of publicly calling for an impeachment inquiry.

His comments come days ahead of Mueller's testimony before the House Judiciary Committee.

There are currently 87 House Democrats backing an impeachment inquiry, according to The Hill's whip list.

The Hill has reached out to Nadler's office for comment.

Speaker Nancy Pelosi Nancy PelosiPelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' On The Money: Anxious Democrats push for vote on COVID-19 aid | Pelosi, Mnuchin ready to restart talks | Weekly jobless claims increase | Senate treads close to shutdown deadline Trump signs largely symbolic pre-existing conditions order amid lawsuit MORE (D-Calif.) has said House Democrats will not proceed with an impeachment inquiry at this time.

Mueller will testify Wednesday in a three-hour hearing before the House Judiciary Committee and two-hour hearing before the House Intelligence Committee regarding allegations of Trump's obstruction of justice outlined in his more than 400-page report.