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.) accused President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE of witness intimidation on Tuesday and threatened legal action to enforce his panel’s subpoena for public testimony from former White House counsel Don McGahn.

"He took to Twitter to call Mr. McGahn a liar. His lawyers went on cable television to do the same," Nadler said at a brief committee hearing that was supposed to feature McGahn’s testimony.

"In short, the president took it upon himself to intimidate a witness who has a legal obligation to be here today," he added. "This conduct is not remotely acceptable."

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Nadler gaveled into the hearing at 10 a.m., despite McGahn’s attorney notifying him late Monday that the former White House official would not appear for public testimony at the direction of the White House.

Trump instructed McGahn to evade the public appearance earlier Monday, citing a Department of Justice legal opinion arguing that he is immune from congressional testimony.

Democrats were irate at the White House’s move, casting it as an effort to obstruct their congressional probes.

Nadler on Tuesday blasted the White House’s legal argument as “baseless” and said the panel would look to “enforce” the subpoena for documents and testimony from McGahn even if it meant going to court. Nadler did not go into further detail on what action the committee would take.

Nadler has previously floated holding McGahn in contempt, as his panel has done with Attorney General William Barr Bill BarrHarris faces pivotal moment with Supreme Court battle Hillicon Valley: DOJ proposes tech liability shield reform to Congress | Treasury sanctions individuals, groups tied to Russian malign influence activities | House Republican introduces bill to set standards for self-driving cars McCarthy threatens motion to oust Pelosi if she moves forward with impeachment MORE for not complying with a subpoena for 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 full report.

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“Our subpoenas are not optional,” Nadler said Tuesday. “Mr. McGahn has a legal obligation to be here for his scheduled appearance. If he does not immediately correct his mistake, this committee will have no choice but to enforce the subpoena against him.”

Tuesday’s hearing lasted less than half an hour.

Rep. Doug Collins Douglas (Doug) Allen CollinsTrump, Biden running neck-and-neck in Georgia: poll Trump, Biden tied in Georgia: poll Loeffler paints herself as 'more conservative than Attila the Hun' in new campaign ad MORE (R-Ga.), the committee’s top Republican, accused Nadler of political theater and said the hearing served no “legitimate legislative purpose” other than to embarrass Trump.

Collins also accused Nadler of refusing to engage in good-faith negotiations with the Justice Department on his subpoena for Mueller’s unredacted report and underlying evidence, suggesting Nadler is instead after the “drama” of holding Barr in contempt.

“Don’t be fooled. The chairman wants the fight and the drama. He does not actually want the information he claims to be seeking,” Collins said. “After the administration made volumes of information available to this committee, the chairman issued overbroad subpoenas and now harangues the administration for being unable to comply with those subpoenas.”

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Nadler subpoenaed McGahn to provide documents and submit to public testimony in April following the release of Mueller’s report, which featured McGahn’s testimony extensively in a section outlining episodes of potential obstruction of justice by Trump.

For Democrats, McGahn is a star witness they can question on Trump's actions with respect to the Mueller investigation. According to Mueller’s report, Trump directed McGahn to have the special counsel removed over alleged conflicts of interest — an instruction he refused.

During his opening remarks Tuesday, Nadler spent several minutes narrating passages from Mueller’s report about McGahn’s interactions with Trump and said that he believes the president would have been charged with a crime had it not been for the Office of Legal Counsel opinion that a sitting president cannot be indicted.

Earlier this month, the White House instructed McGahn not to comply with the document request and demanded Nadler’s committee go directly to the White House with its requests in the future.

The Justice Department opinion cited by the White House on Monday argues that McGahn is not “legally required” to testify about matters related to his work for Trump. It points to precedent under past Democratic and Republican administrations in asserting White House aides cannot be compelled to speak to Congress about their official duties.

“The immunity of the President’s immediate advisers from compelled congressional testimony on matters related to their official responsibilities has long been recognized and arises from the fundamental workings of the separation of powers,” the 15-page letter states.

Democrats’ frustration has been slowly bubbling over as the White House stonewalls their oversight and investigative pursuits, which has prompted more Democratic calls for an impeachment inquiry to begin.

Earlier this month, Judiciary members voted along party lines to hold Barr in contempt of Congress after he did not comply with a subpoena for Mueller’s full, unredacted report and its underlying evidence. The Justice Department has said that doing so would amount to Barr defying the law, and Trump has asserted executive privilege over the subpoenaed materials as a result.

House leaders say they want to wait until after Memorial Day to go after the group of individuals who are refusing to comply with their investigations and who have been given contempt citations.

It is unclear what the next steps will be with respect to McGahn. Nadler warned in a letter to the former White House counsel late Monday that he would face "serious consequences" if he did not show up for the scheduled testimony, adding that the committee "is prepared to use all enforcement mechanisms at its disposal."