(CNN) The House Judiciary Committee is now engaged in a full-blown investigation and legal fight with the goal of deciding whether to recommend articles of impeachment against President Donald Trump by the end of the year, according to Democratic officials involved in the effort.

Recent court filings and public statements by top Democrats point to a dramatic escalation after lawmakers debated internally for months over mounting an impeachment inquiry into the President.

As additional House Democrats continue to call for the House Judiciary Committee to launch an impeachment inquiry — which more than half the caucus now supports — Democratic sources say the issue is essentially moot since what the panel is doing is basically that: investigating whether Trump should be impeached.

The more aggressive posture could help House Democrats convince the courts to side with them in their legal battles with the Trump administration. But it still remains to be seen whether it ultimately leads to the House taking the historic step of making Trump just the third president to be impeached.

House Judiciary Committee Chairman Jerry Nadler backs an impeachment inquiry and has made clear in a series of steps and public statements that he is actively considering recommending articles of impeachment in an attempt to remove Trump from office, something the House made clear in a new lawsuit to force former White House counsel Don McGahn to testify.

"This is formal impeachment proceedings," Nader told CNN's Erin Burnett Thursday on "OutFront."

In the fall, the House Judiciary Committee plans to hold a set of hearings with key witnesses whose testimony would be part of the committee's impeachment deliberations, according to multiple sources.

And after months of resisting formal impeachment proceedings, House Speaker Nancy Pelosi's tone over impeachment has shifted in recent days, endorsing the House Judiciary Committee moves and making clear to her caucus that the panel is considering whether to use its constitutional power to try and remove Trump from office.

What's less clear, is whether Pelosi is simply blessing the moves in an attempt to bolster the House's court cases or if she's seeking to set the stage for impeaching Trump. Publicly, she's not ruling out impeachment.

Nadler, for his part, is making increasingly clear where he stands.

"He has said it many times over the past few weeks now," one source familiar with Nadler's thinking said when asked if he supports an impeachment inquiry. "It's as clear as day."

Impeachment inquiry shifts

Previously, however, Nadler privately pushed Pelosi to support opening a formal impeachment inquiry, making the argument that doing so would improve the House's chances in court. Up until this past month, Nadler had mostly avoided answering questions about whether he backed an impeachment inquiry.

"As I said, we are launching an inquiry now, and whether we'll launch an impeachment inquiry, it may come to that," Nadler said in a June interview with CNN's Wolf Blitzer, drawing a distinction between his committee's investigation and an impeachment inquiry.

Yet at a July hearing, Nadler telegraphed where his committee was going ahead of former special counsel Robert Mueller's testimony, saying, "Articles of impeachment are under consideration as part of the committee's investigation, although no final determination has been made."

Nadler's rhetoric shifted more decisively at the end of last month when his committee petitioned a federal court to provide the House with secret grand jury material from Mueller's investigation. The committee's lawsuit said explicitly that it was conducting its investigation to determine whether to recommend articles of impeachment, and Nadler said it was "in effect" an impeachment inquiry.

"There is one difference which you could draw," Nadler said at a news conference in late July. "If you said that an impeachment inquiry is when you're considering only impeachment, that's not what we're doing. We are investigating all of this and we are going to see what remedies we could recommend, including the possibility of articles of impeachment. We're not limited to that, but that's very much the possibility as a result of what we're doing."

The committee's lawsuit filed Wednesday to obtain testimony from McGahn, who has ignored the committee's subpoena at Trump's direction, was clearer about the aims of the panel's probe, calling him the "most important witness" besides the President himself.

"The Judiciary Committee is conducting an investigation to understand the scope and extent of misconduct by President Trump, and that investigation includes consideration of whether the Judiciary Committee should exercise its Article I powers to recommend articles of impeachment," the lawsuit said.

The complaint continued: "To fulfill its duties, the Judiciary Committee must obtain testimony and evidence from witnesses to the President's actions to determine whether to recommend such articles against the President, or whether to recommend additional or alternative articles that the Judiciary Committee may prepare."

Rep. Doug Collins, the top Republican on the Judiciary Committee, has repeatedly accused Democrats of trying to have it both ways by appearing like they are conducting impeachment proceedings when they are not actually doing so.

More than half of Democrats now back impeachment inquiry

The committee's argument that it's effectively conducting an impeachment inquiry already comes after months of House Democrats slowly growing in numbers backing the formal opening of an impeachment inquiry. Their ranks grew from several dozen in the days after Mueller's May public statement where he emphasized the investigation did not exonerate the President to more than half of the caucus this month.

But the committee is now arguing that the Democrats' calls for an impeachment inquiry are unnecessary.

In court, the Trump administration has argued that the House's subpoenas to date lack a legislative purpose. By asserting the investigation is directly tied to impeachment, the committee has a reason under the constitution to pursue the documents and testimony it's seeking.

Democrats argue that the forthcoming committee hearings will be clearly linked to their impeachment deliberations. In July, the committee voted to authorize subpoenas for 12 individuals, including the President's son-in-law, Jared Kushner. But the committee is considering bringing in officials on their list who did not serve in the White House — which Democrats hope will prevent claims of executive privilege from the White House, although the White House would likely seek to block any discussion about events that took place after the 2016 election.

The committee is expected to issue some those subpoenas in the coming weeks to seek testimony in September and October, potentially to Corey Lewandowski, Trump's former campaign manager; David Pecker, the chairman of National Enquirer parent company American Media Inc.; and Dylan Howard, a lawyer for the women alleging affairs with Trump who received hush-money payments during the 2016 campaign.

Pelosi's shift in tone

Pelosi has shifted her tone over impeachment in recent weeks -- and aides say she's green-lit the language in the House lawsuits that contend the committee is considering voting on whether to impeach the President. She has long contended the House needs to be methodical in its approach, but has consistently batted away talk that the chamber's goal was to impeach Trump, arguing such a move would be divisive and ultimately unsuccessfully since two-thirds of the GOP-led Senate would need to vote to remove Trump from office.

Pelosi's recent posture is different than in March, when she argued that "I don't think we should go down that path" of impeachment, later saying that doing so may not be worth it because it will "end at the Senate's edge." In May, Pelosi claimed the House is "not on a path" to impeachment, arguing to CNN in June that there's "nothing as divisive to the country, in my view, as impeachment."

Since the Mueller testimony, however, she has instead said the focus is on their court battles first, keeping the door more open than she had previously in suggesting the House could impeach Trump. And asked by CNN after the Mueller hearing if she's still concerned that the GOP-led Senate would acquit the President, making impeachment fruitless, she claimed she was "never" concerned about what the Senate would do.

"If we have a case for impeachment that's the place we will have to go," Pelosi said after the Mueller hearing. "But the stronger our case is the worse the Senate will look for just letting the President off the hook."

Recent statements also spotlight Pelosi's difference in tone. In a letter to her caucus this week, she noted the language in the House Judiciary lawsuit, calling it a "significant step" and quoting directly from the suit to say that the House must have all the facts to consider whether to use its constitutional power of "utmost gravity -- approval of articles of impeachment."

Pelosi added: "No one is above the law."

Some Democrats argue that Pelosi may be changing her tune to help their legal case and may ultimately resist moving forward. But it's unclear how she'll come down.

"I think she feels the need to keep the investigative momentum going," said one Democratic lawmaker who is close to Pelosi. "But she's not going to impeachment until she thinks the public is ready."