WASHINGTON — Corey Lewandowski, one of President Trump’s most loyal political confidants, confirmed in congressional testimony on Tuesday that the president had once asked him to help curtail the scope of the Russia investigation, possibly obstructing justice.
But under sharp questioning from Democrats on the House Judiciary Committee conducting an impeachment inquiry, Mr. Lewandowski refused to provide new details about his encounters with Mr. Trump beyond what the special counsel documented. And a combative Mr. Lewandowski, the president’s first campaign manager, insisted that Mr. Trump’s request did not amount to “anything illegal.”
The first in a series of hearings to determine whether the committee should recommend impeachment, the five-hour session brimmed with bitterness and drama. Democrats secured statements they needed from Mr. Lewandowski both confirming his role in Mr. Trump’s attempts to impede the Russia inquiry and vivifying investigators’ accounts with a witness on live television.
Yet the hearing underscored Democrats’ uphill battle as they seek to build a case for impeachment in the face of the entrenched opposition from the White House and potential witnesses. Mr. Lewandowski tried to slow-walk his answers, displayed an attitude of taunting obstinacy and obeyed the White House’s request that he not disclose any private details about his discussions with Mr. Trump. His evasions and occasional outright attacks infuriated Democrats.
Representative Jerrold Nadler, Democrat of New York and the committee’s chairman, told Mr. Lewandowski near the hearing’s conclusion that the panel would consider holding him in contempt of Congress for his refusal to cooperate. But Mr. Nadler trained most of his ire on the White House, mentioning the possibility of drafting an article of impeachment based on its interference in the committee’s investigation.
“The pattern of obstruction laid out in the Mueller report has not stopped,” Mr. Nadler said. “You showed the American public in real time that the Trump administration will do anything and everything in its power to obstruct the work of the Congress.”
One Democrat on the Judiciary panel, Representative Val Demings of Florida, wrote on Twitter during the hearing, “This president must be impeached.”
Democrats’ threats did little to change the reality in the hearing room. Mr. Lewandowski was flanked by two empty chairs meant to be filled by two former senior White House aides, Rick A. Dearborn and Rob Porter, whom the committee had subpoenaed. But late Monday, the White House directed both men not to appear, declaring that they were immune from congressional subpoenas.
Democrats have challenged that assertion in court with regard to another witness, the former White House counsel Donald F. McGahn II, but a ruling could take months, perhaps after the window closes to make an impeachment case before next year’s elections overtake Washington.
Democrats focused during Tuesday’s hearing on trying to draw out details about how Mr. Trump asked Mr. Lewandowski to pressure then-Attorney General Jeff Sessions to diminish the scope of the investigation by the special counsel, Robert S. Mueller III.
Democrats view the episode as an attempt to gut the inquiry, and Mr. Mueller’s investigators suggested that it provided sufficiently plausible evidence of criminal obstruction of justice to present to a grand jury.
As Mr. Mueller recounted, Mr. Trump met with Mr. Lewandowski in the Oval Office in mid-2017 and criticized Mr. Sessions for recusing himself from overseeing the Russia investigation.
The president asked Mr. Lewandowski, a private citizen who has never served in the administration, to deliver a message that Mr. Trump dictated on the spot. Mr. Sessions should give a speech announcing that Mr. Trump had been treated unfairly and that he would limit the scope of the special counsel investigation, the president said.
Mr. Lewandowski made some effort to follow through, setting up a meeting with Mr. Sessions and attempting to enlist Mr. Dearborn, a former Sessions aide, in the task, but ultimately Mr. Lewandowski never conveyed the directive.
Democrats pounced on the strange scenario as evidence that the president was illegally trying to interfere with the inquiry and hide his efforts to do so.
“Didn’t you think it was a little strange the president would sit down with you one-on-one and ask you to do something that you knew was against the law?” asked Representative Steve Cohen, Democrat of Tennessee. “Did that strike you as strange?”
Mr. Lewandowski curtly disagreed: “I didn’t think the president asked me to do anything illegal.”
Pressed about other conversations he may have had with Mr. Trump or other advisers close to the president, Mr. Lewandowski repeatedly declined to answer.
“The White House has directed that I not disclose the substance of any discussion with the president or his advisers to protect executive branch confidentiality,” he said multiple times.
Mr. Lewandowski, who is considering a Senate run in New Hampshire, also used the hearing as an opportunity to promote his allegiance to Mr. Trump in a way that could benefit him politically.
“As for actual ‘collusion,’ or ‘conspiracy,’ there was none,” Mr. Lewandowski said during his opening remarks. “What there has been however, is harassment of the president from the day he won the election.”
Much of his testimony appeared to be calculated to simply irritate or embarrass Democrats, robbing their proceedings of the gravity of impeachment. In his opening remarks, he took a swipe at Hillary Clinton and echoed the president’s apocalyptic and misleading rhetoric “about illegal immigrants pouring across our borders killing innocent Americans.”
During a break that he requested, Mr. Lewandowski tweeted a link to a website for a new super PAC that was created Tuesday, “Stand With Corey.”
Republicans derided Democrats’ investigation as a stunt.
“The majority made a promise: We’ll impeach him. We’ll investigate him. For most of them, it happened in November 2016 because they couldn’t believe Donald Trump won,” said Representative Doug Collins of Georgia, the top Republican on the panel. “And they still can’t get over it today. So what do we do? We have public hearings, lots of flashbulbs, embarrassing the president — not doing an investigation, not doing oversight.”
Democrats intend to stay the course, though divisions persist in their caucus over impeachment.
The Judiciary Committee is sitting on unused subpoenas that it could deploy in the coming weeks compel testimony from a handful of the most prominent Trump administration figures connected to Mr. Mueller’s report, including John F. Kelly, the former White House chief of staff; Jared Kushner, Mr. Trump’s son-in-law and senior adviser; Mr. Sessions; and Rod J. Rosenstein, the former deputy attorney general who appointed Mr. Mueller and oversaw his work.
Democrats will also attempt to broaden their inquiry to other accusations of corruption and malfeasance. On Tuesday, they announced a hearing for next week focused on whether Mr. Trump’s businesses have illegally profited from spending by foreign and domestic government spending in violation of the Constitution’s emoluments clauses.
The committee had also set a deadline Tuesday for homeland security officials to produce any relevant documents related to reported meetings in which Mr. Trump dangled pardons for any officials fearful that they might break the law by implementing his policies at the border. It was not immediately clear whether the administration complied.
Maggie Haberman, Catie Edmondson and Mark Mazzetti contributed reporting.