Nadler, who appealed to the speaker that the House's court cases against the Trump administration would be bolstered by launching an impeachment inquiry, also offered two new arguments in the hopes of convincing Pelosi from moving off her steadfast opposition, according to a source with knowledge of the meeting.

First, Nadler argued opening an impeachment probe would centralize the House's sprawling investigations now spread across various panels into just one: The House Judiciary Committee. He argued that the other committees looking into various Trump controversies and scandals could instead focus on moving the party's legislative agenda, while his panel -- with its unique expertise -- would investigate the alleged crimes of Trump before deciding whether to formally vote on articles of impeachment.

Secondly, Nadler made a technical argument that it would be easier for lawmakers to discuss the President's alleged offenses on the House floor and in committees during a formal impeachment inquiry because House rules forbid members from disparaging individuals.

But Nadler met powerful resistance.

First was from Pelosi, who said she would rather see Trump "in prison" than impeached, according to Politico. He was also rebuffed by House Intelligence Chairman Adam Schiff, who himself is also playing a major role investigating Trump and his conduct while in office, according to another source familiar with the matter.

The previously unreported details on Nadler's pitch to Pelosi offer new insight into the under-the-radar effort by the House Judiciary chairman to try to sway the speaker to reconsider her opposition to launching an impeachment probe. It comes amid a fierce debate among congressional Democrats and presidential hopefuls about whether to impeach the President heading into the 2020 campaign.

Pelosi's opposition has forced Nadler into a difficult position. He is stuck between the vocal demands from members on his committee who want to open a probe and his personal belief that doing so is worthwhile. At the same time, he does not want to appear disloyal to the most powerful in Democrat in Congress who believes launching impeachment proceedings would be fruitless with the Senate unwilling to convict the President.

"He's been very careful in advocating the view of the committee," said one Democratic Judiciary member. "But he doesn't want to throw (Pelosi) under the bus."

Publicly, Nadler has argued that beginning an impeachment inquiry would bolster the House's hand with federal judges in the Democrats' court battles against the Trump administration — because Congress has a right to more documents while undertaking a judicial proceeding — amid fears that a loss in court would dramatically expand the power of the White House at the expense of Congress.

But Pelosi has rejected that notion, pointing to the House's victory in two major court fights to obtain Trump financial records.

Privately, Nadler has been supportive to members on his committee who have publicly announced their backing for an impeachment probe, according to Democratic sources. Nadler has been careful to not go too far in flatly accusing the President of conduct that warrants impeachment, leaving that to other members, TV commentators and major newspaper editorial boards instead.

Nadler declined to be interviewed for this article. A Nadler spokesperson said, "As Chairman Nadler has said many times, the President's conduct makes it impossible to rule anything out and no option is off the table. It is imperative that the obstruction of justice, public corruption and other abuses of power by the President, his associates and his administration are fully investigated and that there is accountability and transparency with the American people. That is something the entire Democratic Caucus believes strongly. No one, not even the President, is above the law."

But the gulf between him and Pelosi was on display during an exchange with CNN's Wolf Blitzer on Wednesday

Asked if he and Pelosi were on the same page over an impeachment inquiry, Nadler looked down, paused for a few seconds and said: "As I said, we are launching an inquiry now, and whether we'll launch an impeachment inquiry, it may come to that."

Asked later if he would ever break from Pelosi and open an impeachment probe without her support, Nadler said: "When that decision has to be made, it will be made not by any one individual, it will be made probably by the caucus as a whole. Certainly, Nancy will have the largest single voice in it, (and) various committee chairs and rank-and-file members."

Pelosi spokeswoman Ashley Etienne said the speaker and committee chairs had a productive meeting where they agreed "to keep all options on the table and continue to move forward with an aggressive hearing and legislative strategy." A Schiff spokesman declined to comment.

Members of the House Judiciary Committee have become increasingly adamant in calling for impeachment, something that was voiced in a private May 20 meeting in the Rayburn House Office Building. In the meeting, sources said, more than half a dozen members made the case to open up an impeachment inquiry, with just one member -- Rep. Zoe Lofgren -- voicing her opposition.

Nadler, listening to his members' concerns, said he would take their views directly to Pelosi that night. But after sitting down in the speaker's office, Pelosi rejected the call from Nadler and committee Democrats.

Afterward, Nadler convened a late-night conference call with his members to tell them the view of the speaker. According to multiple participants on the call, Nadler told his members that they would ramp up their existing probe into potential obstruction of justice at the White House, issuing more subpoenas if they have to, holding more officials in contempt and trying to shed more light on the details on the Mueller report than they have so far.

But Nadler has said he has a three-part test to determine whether impeachment is warranted: Namely whether impeachable offenses have been committed; whether those offenses are serious enough to warrant the removal of a president; and whether the country will determine at the end of the process that it has not been a partisan exercise.

Many Democrats are already there. Rep. Jamie Raskin, a Maryland Democrat on the Judiciary Committee who backs beginning an inquiry, said this week there's "growing sentiment this is an intolerable situation."

Rep. Lloyd Doggett, a Texas Democrat, called it "long past time" to open an impeachment inquiry.

"I think the speaker is rightfully cautious, she has to work with our entire caucus," Doggett said. "She also did not have the benefit of knowing in advance what total obstruction Donald Trump would insist upon. ... So now that she has that information I hope she'll be joining us in encouraging the prompt institution of impeachment proceedings."

What has Nadler and other Democrats nervous about Pelosi's strategy -- to maintain the investigations methodically and fight individual battles in court -- is the fear that they could lose a court case, and set back their efforts dramatically. Just this week, a federal judge denied House Democrats' lawsuit to block the President from transferring funds to build the border wall, saying that the House lacked standing to bring the challenge and that the court should not step in the middle of the fight between the President and Congress.

It's raised fears that similar rulings could hamstring the Democrats' efforts to enforce their subpoenas through the courts after the White House has refused to cooperate with Democratic investigations.

Still, Pelosi is quick to organize her supporters against restlessness in her caucus. She easily fought back a challenge to her leadership after Democrats won control of the House in 2018, and she's kept her top lieutenants behind her strategy that it's too soon to start an impeachment inquiry. When impeachment advocates grew restless last month after McGahn refused to appear under subpoena, she held a caucus-wide meeting where key committee chairmen — including Nadler — outlined their investigative work and victories in court.

"I'm absolutely in support of the speaker's direction. I think we need to have all of our ducks lined up in a row. We're not there yet," said Rep. Karen Bass, a Judiciary Committee member who leads the Congressional Black Caucus. "We've already had two favorable court decisions, so I think we're on the right path."