Nearly half of House Democrats are now on board with an impeachment inquiry, in a sign that Robert Mueller's faltering testimony last week did little to dissuade lawmakers who had been on the fence about activating the highly controversial process against President Trump.

While confusion hangs over what exactly Democrats are pursuing, several have indicated they see their investigation as the prelude to a decision on whether to recommend articles of impeachment at the committee level.

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And the number of Democrats, including senior members, endorsing the process has only grown since last week. As of Wednesday, at least 113 Democrats, and independent Rep. Justin Amash, have come out in support of an impeachment inquiry—including 15 members of the House Judiciary Committee that would oversee the proceedings. There are 235 Democrats in the House.

The latest big name to call for an impeachment inquiry was House Foreign Affairs Committee Chairman Eliot Engel, D-N.Y., who broke with other House leaders, including Speaker Nancy Pelosi, D-Calif., who have declined to endorse the process at this stage.

“The American people want, and deserve, the truth,” Engel wrote on Twitter. “I believe the House must pursue a formal impeachment inquiry.”

In an attached statement, Engel said the president has “abused the power of his office in an effort to stymie a legitimate investigation into his campaign’s involvement with Russia.”

The mounting calls come after Democrats on the House Judiciary Committee said last week they were proceeding with what they called an “impeachment investigation,” as they insisted former Special Counsel Mueller delivered damning testimony against Trump in last week’s hearings—despite concerns from many on the left that his appearance was faltering and broke little new ground.

Committee Chairman Jerrold Nadler, D-N.Y., as a major next step, filed a petition in D.C. federal court to obtain grand jury materials from the former special counsel’s investigation. The petition claimed that the committee needed the information in order to determine whether to recommend articles of impeachment, in an attempt to give the request more weight in the eyes of the court.

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Nadler called the grand jury materials “critically important” for their investigation. In the petition, Democrats on the committee noted that because Justice Department policies do not allow the prosecution of a sitting president, the House of Representatives is “the only institution of the federal government” that can hold Trump accountable.

It is unclear what new information might be found in the grand jury transcripts. Many of the high-profile witnesses connected to the White House, for instance, appeared for voluntary questioning before Mueller’s team rather than before the grand jury.

Trump, meanwhile, declared the Mueller testimony a "bust" while saying nothing will ever be "good enough" for Democrats determined to go after him.

"Robert Mueller’s testimony, and the Mueller Report itself, was a disaster for this illegal Democrat inspired Witch Hunt," he tweeted afterward.

Since Mueller’s testimony before both House Judiciary and Intelligence Committees last Wednesday, 20 House members have voiced their support for an impeachment inquiry.

Nadler claimed Mueller’s report showed the Trump campaign welcomed Russian interference in the 2016 election and Trump “repeatedly lied to cover it up”—and that Mueller’s testimony “removed all doubt” about those points.

Mueller stood by his team’s findings at last week’s hearings—reiterating that the special counsel’s office found no evidence of a criminal conspiracy between Trump associates and Russia, while also stating that the president was not exonerated on allegations of obstruction of justice despite his assertions to the contrary.

But in doing so, he also repeatedly refused to drift beyond the bounds of his report.

This was, to an extent, expected as Mueller had signaled he would only address material already in the public record.

Meanwhile, Republicans on the House Judiciary Committee are arguing that an impeachment inquiry is “not an official thing,” and said that the court filing for grand jury materials is only part of a Democratic inquest “to determine if they should recommend articles of impeachment.”

Committee Ranking Member Doug Collins, R-Ga., said that Democrats have “no right” to the grand jury materials to begin with.

“Chairman Nadler’s legal action here is sure to fail, weakening Congress’s ability to conduct oversight now and into the future. If my colleagues want grand jury information, they should propose legislation allowing Congress to access it,” he said in a statement. “Democrats want to convince their base they’re still wedded to impeachment even after [last week’s] hearing, but a baseless legal claim is an odd way to show that.”

But even as his committee proceeds with court filings and their Trump-focused investigation, Nadler has danced around whether Democrats are officially running an impeachment inquiry.

"We have impeachment resolutions before the committee. We are conducting investigations to determine whether we should report those impeachment resolutions to the House or direct our own and report those to the House. We're considering those resolutions," Nadler said on ABC's "This Week" Sunday. "We'll make a determination after we get more evidence as to the president's crimes that we had from the Mueller report and also from other things."

He added: "We're investigating whether to report -- whether to approve articles of impeachment before the committee."

And despite her public reluctance to proceed with impeachment, Pelosi said she is keeping options open.

"Let's get sophisticated on this," she said last week. "We will proceed when we have what we need to proceed--not one day sooner."

Fox News' Chad Pergram contributed to this report.