WASHINGTON — The White House on Monday blocked two more former aides to President Trump from testifying in House Democrats’ impeachment inquiry, but cleared a third witness, Corey Lewandowski, to appear publicly on Tuesday and answer questions about potential obstruction of justice by the president.
The White House decisions amounted to mixed news for the House Judiciary Committee as it tries to crank up the intensity of an investigation devised to determine whether to recommend Mr. Trump’s impeachment for obstruction of justice and abuse of power — and to convince the public that such action is warranted.
In Mr. Lewandowski, who managed Mr. Trump’s presidential campaign and remained a confidant — albeit from a distance — once he became president, the judiciary panel will be getting a figure who could help bring to life evidence uncovered by Robert S. Mueller III, the special counsel who investigated Russia’s interference in the 2016 election. Though the panel has publicly quizzed legal experts and Mr. Mueller on his findings, Mr. Lewandowski will be the first fact witness referenced in Mr. Mueller’s report whom the White House has not blocked from publicly testifying.
He played an important role in an attempt by the president in summer 2017 to effectively end scrutiny of Mr. Trump’s campaign, one of several episodes that Democrats have said were clear cases of obstruction. Mr. Lewandowski is also pugnacious, fiercely loyal to Mr. Trump and contemplating a Senate run in New Hampshire — and he is likely to arrive on Capitol Hill intent on undercutting Democrats’ case.
The White House ordered two other former aides to Mr. Trump, Rob Porter and Rick A. Dearborn, not to appear before the Judiciary Committee, a move that will only compound a fight playing out in the courts over whether Mr. Trump can continue to effectively stonewall attempts by Congress to investigate his administration, including by refusing to allow current and former officials to testify.
On Monday, the White House counsel, Pat A. Cipollone, wrote to Mr. Lewandowski and the committee saying that he would be free to discuss his work on the Trump campaign and matters that have already been made public by Mr. Mueller, but not any other additional communications he may have had with Mr. Trump. As senior White House aides, Mr. Porter and Mr. Dearborn were “absolutely immune” from congressional testimony, he said in another letter.
Tuesday’s hearing is shaping up to be an important test for Democrats as they struggle to engage and retain the public’s attention with what they argue is ample evidence of obstruction of justice and abuse of power by Mr. Trump. It comes as Democrats’ messaging on impeachment is increasingly muddled, with leaders saying they have not reached the threshold and other Democrats arguing that the process is well underway.
Representative Jerrold Nadler, Democrat of New York and the chairman of the Judiciary Committee, sought on Monday to clear up lingering questions about the seriousness of his panel’s work.
“Personally, I think the president ought to be impeached,” Mr. Nadler said during an interview on WNYC in New York. But, he conceded, the House was still divided on that point and would not advance impeachment articles unless it could win over public support in sessions like the one expected on Tuesday.
“The American people have to be educated and they have to be convinced,” he said. “We cannot impeach the president against the will of the American people.”
To that end, Democrats are likely to use most of their questioning on Tuesday to spotlight a scheme in which the president enlisted Mr. Lewandowski to try to curtail the special counsel investigation, one of 10 possible acts of obstruction detailed by Mr. Mueller. They may also ask Mr. Lewandowski about his knowledge of the Trump campaign’s contacts with Russians, and how it viewed the Russian interference campaign.
The attempts to influence Mr. Mueller’s work occurred in June and July 2017, not long after Mr. Trump ordered Donald F. McGahn II, the former White House counsel, to fire Mr. Mueller, a command he refused.
In this case, the report says the president “dictated a message” to Mr. Lewandowski that he wanted him to deliver to Jeff Sessions, the attorney general. The message instructed Mr. Sessions, who was recused from the matter, to state publicly that the special counsel’s investigation was “very unfair,” and then to significantly narrow its scope to prevent future interference, effectively ending the investigators’ scrutiny of Mr. Trump’s campaign.
Mr. Trump followed up about a month later, and Mr. Lewandowski indicated he would deliver the message soon. He did not, however, and instead asked Mr. Dearborn, a former aide to Mr. Sessions then working in the White House, to do so instead. Mr. Dearborn, too, was uneasy about the request, and Mr. Mueller wrote that he never delivered it.
Because of a Justice Department policy that prohibits charging a sitting president, Mr. Mueller ultimately did not decide one way or another whether Mr. Trump’s actions amounted to criminal obstruction of justice.
While the report does not detail any instances in which Mr. Porter was involved in the president’s efforts to limit the scope of Mr. Mueller’s work, his job put him in proximity to Mr. Trump and made him aware of the flow of information coming in and out of the Oval Office. As staff secretary, Mr. Porter’s notes from the White House are frequently referenced in Mr. Mueller’s report.
Mr. Trump, for his part, continues to rail against congressional investigators, whose work he has portrayed as a desperate attempt to take down an innocent man. On Monday, he wrote in a series of tweets that Democrats had “given up” on the findings of the Mueller report and were hunting through “everything else” about him to try to make their case.
He urged the committee instead to begin looking into lucrative book and television deals signed by his predecessor, Barack Obama, and other Democrats. “Those investigations would be over FAST!”
As Tuesday’s hearing was expected to demonstrate, Democrats continue to see Mr. Mueller’s findings as a central part of their impeachment investigation. But they have begun broadening their scope this fall in an effort to evaluate the severity of other potential offenses, including whether Mr. Trump’s businesses have profited from spending by foreign or domestic government entities in violation of the Constitution’s emoluments clauses.
The committee has set an additional deadline for Tuesday on another area of scrutiny: reports that Mr. Trump has dangled pardons to immigration officials willing to carry out his policies at the border even if they break the law. Homeland security officials are under subpoena to hand over documents relevant to several reported episodes on Tuesday. However, Mr. Trump has denied he ever offered pardons, and the White House has said that in at least one case, he was merely joking, making the department’s response uncertain.