Democrats on the House Judiciary Committee are headed for a confrontation with the White House after setting a series of key deadlines this week for documents and witness hearings.

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.) set Tuesday as the deadline for three witnesses to provide testimony at a hearing and for the Department of Homeland Security to provide materials on whether 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 dangled pardons to border officials.

So far, former Trump campaign manager Corey Lewandowski Corey R. LewandowskiTrump faces tricky choice on Supreme Court pick How Trump can win reelection: Focus on Democrats, not himself Trump Jr. distances from Bannon group, says he attended 'single' event MORE is the only witness to agree to attend the hearing that is expected to focus on a key episode of possible obstruction by Trump, as laid out in 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.

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But Democrats say the White House made the unprecedented step late Monday night in seeking to limit the testimony of someone who has never served in the administration, by claiming such discussions fall under "Executive Branch confidentiality interests."

"Mr. Lewandowski's conversations with the President and with senior advisers to the President are protected from disclosure by long-settled principles protecting Executive Branch confidentiality interests and, as a result, the White House has directed Mr. Lewandowski not to provide information about such communications beyond the information provided in the portions of the Report that have already been disclosed to the Committee," White House counsel Pat Cipollone wrote in a letter to Nadler.

Also late Monday evening, Nadler announced that the White House blocked former White House aides Rob Porter and Rick Dearborn from testifying, citing claims of immunity, which follows the administration's game plan of blocking the testimony of former and current administration officials.

Nadler in response blasted the White House, describing their latest moves as a "shocking and dangerous assertion of executive privilege and absolute immunity.

"The President would have us believe that he can willfully engage in criminal activity and prevent witnesses from testifying before Congress--even if they did not actually work for him or his administration," Nadler said in a statement Monday night. "If he were to prevail in this cover-up while the Judiciary Committee is considering whether to recommend articles of impeachment, he would upend the separation of powers as envisioned by our founders."

Even with the limitations, Lewandowski has vowed to come out swinging on behalf of his former boss, raising questions about whether the committee’s first fact witness will cooperate with questioning as the panel seeks to investigate obstruction, public corruption and other alleged abuses of power.

According to a source familiar with the matter, the committee is preparing for the president’s longtime confidant to be a combative witness.

The eleventh hour claims of privilege are poised to exacerbate the standoff between the White House and House Democrats, particularly after their battle took a new turn on Friday when the Department of Justice (DOJ) urged a federal judge to throw out Democrats’ lawsuit seeking access to grand jury material that was redacted in the Mueller report.

Judiciary Democrats have hoped that describing their investigation as a formal impeachment probe in court filings will boost their standing in court and give them access to information like grand jury material before deciding whether to introduce articles of impeachment against Trump.

But the DOJ argued in Friday’s filing that House Democrats have offered conflicting messages about the state of their investigation.

DOJ attorneys pointed to remarks made by Speaker Nancy Pelosi Nancy PelosiDemocratic senator to party: 'A little message discipline wouldn't kill us' Overnight Health Care: New wave of COVID-19 cases builds in US | Florida to lift all coronavirus restrictions on restaurants, bars | Trump stirs questions with 0 drug coupon plan Overnight Defense: Appeals court revives House lawsuit against military funding for border wall | Dems push for limits on transferring military gear to police | Lawmakers ask for IG probe into Pentagon's use of COVID-19 funds MORE (D-Calif.) and House Majority Leader Steny Hoyer Steny Hamilton HoyerHouse to vote on resolution affirming peaceful transition of power 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 Vulnerable Democrats tell Pelosi COVID-19 compromise 'essential' MORE (D-Md.) that contradicted comments made by Nadler and other Judiciary Democrats that they are in “formal impeachment proceedings.”

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“The Committee’s own description of its investigation makes clear that it is too far removed from any potential judicial proceeding to qualify,” DOJ said in its filing. “Most prominently, the Speaker of the House has been emphatic that the investigation is not a true impeachment proceeding.”

“Nor does the Committee provide any basis to distinguish its current ‘investigation’ from the sort of oversight that Congress routinely undertakes, all of which could potentially lead to the impeachment of Executive Branch officials,” DOJ added.

Democrats have offered descriptions of being in an impeachment process, an impeachment investigation and an impeachment inquiry, with some using the word “formal” while others in the party dispute that characterization.

The widespread disagreement among Democrats about the state of the investigation has caused confusion as members seek to lay out their strategies to the public.

Impeachment for Pelosi is a numbers game, and polls consistently show that a majority of voters do not support going down that road.

Nadler, however, has said he believes Trump should be impeached as a way of condemning him for his conduct, stating that he does not believe the GOP-controlled Senate would support his removal.

“Personally, I think the president ought to be impeached,” Nadler told WNYC on Monday. “Impeachment is imperative not because he’s going to be removed from office — the Senate won’t do that — but because we have to vindicate the Constitution.”

The recent pushback from the DOJ comes as the White House has hampered Democrats’ investigative efforts by making claims of executive privilege, arguing that under the standard of immunity, confidentiality protections offered to the executive branch apply to current and former aides, effectively preventing them from disclosing what took place during their time in the administration.

While both Republican and Democratic administrations have invoked the immunity concept, legal experts say there is virtually no case law on the subject, with some predicting the White House is likely to lose if it’s challenged in court.

Democrats have sought to challenge the administration by filing a lawsuit to enforce the subpoena against former White House counsel Don McGahn, who Democrats have described as their “most critical witness.”

If the court rules in their favor, Democrats hope the McGahn case will trigger a domino effect by compelling other witnesses who have obeyed White House orders not to testify on Capitol Hill.

And while Judiciary Democratic counsels have offered an optimistic timeline that the case will be settled this year, legal experts say that’s unlikely, particularly if the losing side chooses to go through the appeals process.

Lewandowski, who is considering a 2020 run against Democratic Sen. Jeanne Shaheen Cynthia (Jeanne) Jeanne ShaheenSenate Democrats introduce bill to sanction Russians over Taliban bounties Trump-backed candidate wins NH GOP Senate primary to take on Shaheen Democratic senator urges Trump to respond to Russian aggression MORE (N.H.), is considered an important witness because he was involved in a key episode of possible obstruction by Trump that Mueller examined that also ties in Dearborn.

According to the Mueller report, when Trump discovered the now-former special counsel was investigating him for possible obstruction, in addition to probing whether members of the Trump campaign coordinated with Russia in 2016, he ordered McGahn to remove Mueller over alleged conflicts of interest. Around that same time, Trump also asked Lewandowski to persuade then-Attorney General Jeff Sessions Jefferson (Jeff) Beauregard SessionsRoy Moore sues Alabama over COVID-19 restrictions GOP set to release controversial Biden report Trump's policies on refugees are as simple as ABCs MORE to reverse his recusal and set new limits on the Mueller probe.

Lewandowski appealed to Dearborn, then-White House deputy chief of staff, to pass along a written message to Sessions, according to the 448-page Mueller report. Ultimately, Dearborn did not carry out those orders.

And separately, Trump also reportedly attempted to change the narrative by ordering Porter to create a record refuting McGahn's account.

Lewandowski is no stranger to Capitol Hill testimonies after appearing several times last year to testify about Russian interference. His first appearance before the House Intelligence Committee sparked angry condemnations from Democrats after he stated that he was not prepared to answer questions that related to anything after he left the Trump campaign in the summer of 2016, including his time on the Trump transition team.

During his second appearance in March 2018, Lewandowski further infuriated Democrats by using profanities in the middle of a closed-door hearing, in what he described as frustration over their repeated attempts to get him to respond to questions of coordination with Russia.

This week’s subpoena deadline for Lewandowski and others comes as the Judiciary Committee’s sprawling probe is burgeoning to include a range of other issues that Nadler says will help Democrats determine whether to introduce articles of impeachment against Trump.

This includes whether Trump violated the Emoluments Clause of the Constitution by profiting off government spending after Vice President Pence, other administration officials and Air Force officials stayed at his family-owned resorts.

While the president and his GOP allies have accused Democrats of conducting partisan investigations that aim to hurt Trump heading into 2020, Democrats say they are still examining obstruction, which includes Lewandowski’s testimony on Tuesday.

But Lewandowski has hinted that he will use the public appearance as an opportunity to blast Democrats.

“I want to go and remind the American people that these guys are on a witch hunt, right?” he told Fox News Radio last month.