House Democrats filed a lawsuit in federal court on Friday to obtain the grand jury materials from former Special Counsel Robert Mueller’s report into Russian interference in the 2016 election, arguing that they needed the information to determine whether to recommend articles of impeachment to the lower chamber.

Aides on the Judiciary Committee characterized the lawsuit as the strongest step yet toward launching impeachment proceedings against President Donald Trump. “In the most formal and official way a committee can, we have just given notice that we are actively considering articles of impeachment,” said one House Judiciary Counsel. “That is as serious a step as we can take at this time.”

House Speaker Nancy Pelosi, who for months has been resisting calls from her members to take more concrete action towards impeachment, approved the lawsuit, according to aides.

The lawsuit, which was filed by House General Counsel Doug Letter in the U.S. District Court for the District of Columbia on Friday, seeks all of the materials from the report that the Department of Justice redacted under the federal rules of criminal procedure. In making the case to obtain the materials, the Democrats note that the information could be key to making a determination on pursuing impeachment.

“Because Department of Justice policies will not allow prosecution of a sitting president, United States House of Representatives is the only institution of the federal government that can now hold President Trump accountable for these actions,” the filing reads. “To do so, the House must have access to all the relevant facts and consider whether to exercise is full article one powers, including a constitutional duty power of the utmost gravity recommendation of articles of impeachment.”

In total, the word “impeachment” is mentioned 76 times in the filing.

The White House and the Department of Justice didn’t immediately respond to a request for comment.

Typically, grand jury materials must be kept confidential, but there can be exceptions for release when they are needed for judicial proceedings. Democrats argue in the filing that an impeachment trial would fall under that category, thereby making it necessary for them to obtain the documents. “This Court is authorized to disclose these materials pursuant to Rule 6(e)(3)(E) because the Committee seeks to use them “preliminarily to or in connection with a judicial proceeding,” the filing states. “The D.C. Circuit has construed that provision to apply where, as here, this Committee is conducting an investigation to determine whether to recommend articles of impeachment.”

The filing also notes that, given the components of Mueller’s report that deal with election interference, which falls under the jurisdiction of the House Permanent Select Committee on Intelligence, the Judiciary will work closely with them in determining their recommendation on impeachment.

A spokesperson for the Intelligence Committee declined to comment beyond the filing.

The official request for grand jury material was one of two steps Nadler had announced earlier this week as part of his committee’s path forward in the aftermath of Mueller’s testimony. The other component was to compel the appearance of Don McGahn, the former White House counsel who defied a Congressional subpoena at the direction of the Trump Administration. Nadler said the committee is still negotiating with McGahn and would file a second lawsuit if accommodations could not be reached “In very short order.”

Judiciary aides emphasized that McGahn’s appearance would be critical for determining an impeachment recommendation. McGahn was a key witness for Mueller and a major actor in his report, and Democrats have honed in on two incidents Mueller laid out involving him: Trump urging him to fire Mueller, and subsequently telling him to deny media reports that he told him that.

McGahn’s attorney did not immediately respond to a request for comment.

Friday’s announcement, which coincided with the start of a six-week long Congressional recess, appeared to largely satisfy committee members and other lawmakers who had been pushing for more action on the impeachment front.

“We’re crossing a threshold, absolutely,” said Texas Rep. Veronica Escobar, who sits on the committee and has come out in favor of an impeachment inquiry. “We are now officially entering into an examination of whether or not to recommend articles of impeachment.”

Republicans cast the move as entirely political. “Democrats want to convince their base they’re still wedded to impeachment even after this week’s hearing, but a baseless legal claim is an odd way to show that,” Rep. Doug Collins, the ranking member on the Judiciary Committee, said in a statement.

Seeking this material, however, hardly means any impeachment action is imminent. The House of Representatives do not return to the Capitol until the second week in September, making it unlikely that anything major would happen before then. And while counsels on the Judiciary Committee expressed confidence they would ultimately obtain these materials, they could not provide any timeline for when it would happen.

Write to Alana Abramson at Alana.Abramson@time.com.