House Democrats are accelerating and expanding their Trump-focused investigations as they return from summer recess, as President Trump rejects the latest round of ethics complaints and his allies warn that the ever-multiplying probes could derail the Democrats' legislative agenda.

In the latest major development, House Judiciary Committee Chairman Jerrold Nadler, D-N.Y., announced a vote for later this week that will essentially formalize the early stages of impeachment proceedings following weeks of confusion. A committee vote is scheduled for Thursday to set the rules for future hearings in its investigation to determine whether to recommend articles of impeachment against the president.

DOUG COLLINS CALLS HOUSE DEMS 'PITIFUL' FOR IMPEACHMENT PUSH

“The unprecedented corruption, coverup, and crimes by the President are under investigation by the Committee as we determine whether to recommend articles of impeachment or other Article 1 remedies,” Nadler said in a statement Monday. “The adoption of these additional procedures is the next step in the process that will help ensure our impeachment hearings are informative to Congress and the public, while providing the President with the ability to respond to evidence presented against him.”

He added: “We will not allow Trump’s continued obstruction to stop us from delivering the truth to the American people.”

The new procedures would empower Nadler to hold full or subcommittee hearings as part of the impeachment investigation. Nadler also announced that the committee will hold a hearing for former Trump campaign manager Corey Lewandowski—whom they subpoenaed last month—on Sept. 17.

Republicans panned the new efforts as yet another bid to go after Trump, after hearings starring witnesses ranging from former Special Counsel Robert Mueller to ex-Trump lawyer Michael Cohen failed to deliver a political deathblow.

“That doesn’t stop them,” Rep. Jim Jordan, R-Ohio, a member of the Judiciary Committee, told Fox News on Monday. “They’re going to continue to push this ridiculous impeachment narrative.”

Jordan also suggested that Democrats should call Justice Department Inspector General Michael Horowitz, who has been looking into the origins of the Russia investigation and potential abuses of the Foreign Intelligence Surveillance Act (FISA), while suggesting that Democrats are not focused on their legislative agenda.

“They’re so focused on impeachment, they’re missing, I think, the important things,” Jordan said.

The focus on an array of Trump investigations threatens to overshadow the Democratic agenda, even as House Speaker Nancy Pelosi has tried to focus on policy items like gun control and prescription drug prices. Last week, House Majority Leader Steny Hoyer, D-Md., sent a memo outlining the agenda for the party this fall -- including votes on bills to block offshore drilling, to boost funding for the National Flood Insurance Program, and more.

Pelosi, D-Calif., has been cool to the idea of impeachment all along, amid concerns that the focus could hurt some members politically. Pelosi has suggested the public generally does not support impeachment, and many moderate Democrats have also distanced themselves from the process, saying there is no chance of obtaining a two-thirds vote in the Republican-controlled Senate necessary to convict and remove Trump from office.

“I’ve been traveling all of August,” Rep. Henry Cueller, D-Texas, said last week. “This is not an issue people bring up. I think a lot of people would rather just vote him out, vote the president out.”

HOUSE DEMS INVESTIGATE PENCE STAY AT TRUMP'S DOONBEG RESORT

And 2020 presidential hopeful Rep. Tulsi Gabbard, D-Hawaii, said in an interview that impeachment proceedings would “tear our country apart.”

The issue of impeachment has not been a top priority for voters. In June, a Fox News poll showed that most Americans didn’t think impeachment was in the president’s future and did not want him impeached and removed from office.

Last month, though, a Fox News poll showed growing public support on another hot-button issue: gun control. Bipartisan majorities of voters have favored background checks on gun buyers and taking guns from people who have posed dangers to themselves or others, the poll found.

Democrats have said a top priority this session would be to seek a Senate vote on what they called “the much-needed, House-passed Bipartisan Background Checks Act.” That bill was passed by the House in February and would require background checks on all gun sales, including those between strangers meeting online or at gun shows.

Currently, the National Instant Criminal Background Check System (NICS) has been employed for sales involving licensed firearms dealers, constituting the majority of all firearm sales.

But the impeachment and investigation agenda threatens to soon be all-consuming.

More than half of the 235 House Democrats support launching a formal impeachment inquiry into the president. The escalation in support for impeachment proceedings came after Mueller delivered testimony on Capitol Hill before both the House Judiciary and House Intelligence Committees. Many felt that they were given little new material to fuel a case for impeachment after Mueller’s back-to-back hearings, but Nadler defended it as “an inflection point.”

Committee Ranking Member Doug Collins, R-Ga., called the efforts “pitiful.”

“[Nadler] is trying to pull a fast one on the American people again. They know they don’t have the votes to go for a full, formal impeachment inquiry,” Collins said on “Fox & Friends” Monday. “They want to continue to put a false narrative out there…it’s really become a pitiful scene.”

The Judiciary Committee has pivoted to focus not just on Trump's alleged obstruction of justice in the Russia investigation, but also the Trump administration’s use of Trump Organization properties, which they claim violate the Emoluments Clause and could feed their case for impeachment.

Last week, Nadler penned a letter to White House Counsel Pat Cipollone and Secret Service Director James Murray seeking information about Trump’s “apparent promotion and solicitation of foreign and U.S. government business at Trump Organization owned or affiliated properties.”

Nadler claimed that Vice President Mike Pence’s latest stay at Trump’s resort in Doonbeg, Ireland, as well as the president’s proposal to host the 2020 G-7 summit at Trump National Doral Golf Club outside of Miami, were “potential violations of the Foreign and Domestic Emoluments Clauses of the Constitution,” and noted that they are “of significant interest and grave concern to the Committee as it considers whether to recommend articles of impeachment.”

“The Doral and Doonbeg cases are just two of the many examples of the solicitation or receipt of foreign government spending to the benefit of the President’s private financial interests,” Nadler wrote. “The impact that the President’s business interests may have on his official conduct and American foreign policy interests demands scrutiny by Congress—as does the use of taxpayer dollars on properties or businesses benefitting the president.”

House Oversight Committee Chairman Elijah Cummings, D-Md., also took issue with the Doonbeg stay and requested documents and “itemized costs” associated with the visit, from the White House and the Trump Organization.

Meanwhile, the administration is battling criticism over an Air Force stopover in Scotland, which included a stay for crew members at Trump Turnberry Resort. The Air Force has defended the stay as “the closest available and least expensive accommodations.”

Trump, though, has dismissed the criticisms, saying he had “nothing to do” with either Pence’s stay in Doonbeg or the Air Force’s stop at Turnberry.

“I know nothing about an Air Force plane landing at an airport (which I do not own and have nothing to do with) near Turnberry Resort (which I do own) in Scotland, and filling up with fuel, with the crew staying overnight at Turnberry (they have good taste!). NOTHING TO DO WITH ME,” Trump tweeted on Monday.

Minutes later, he tweeted again, addressing Pence’s stay at his resort in Ireland last week.

“I had nothing to do with the decision of our great @VP Mike Pence to stay overnight at one of the Trump owned resorts in Doonbeg, Ireland. Mike’s family has lived in Doonbeg for many years, and he thought that during his very busy European visit, he would stop and see his family!”

Last week, Pence defended his stay, saying the Doonbeg resort was “logical” and he had family ties to the village. Pence also said that the State Department “approved us staying there” before he officially booked his stay.

Pence’s chief of staff Marc Short originally said that the president made a “suggestion” for Pence to stay at his resort. But later, Short retracted his comments, instead saying that “at no time did the president direct our office to stay at his Doonbeg resort, and any reporting to the contrary is false.”

Trump, last week, denied that he ever even spoke to Pence about the trip.

“I don’t suggest anything,” Trump said.

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Also on Monday, the House Intelligence, Oversight, and Foreign Affairs Committees on Monday launched a separate investigation into the president -- this time, focused on Trump and personal lawyer Rudy Giuliani's alleged efforts to pressure the government of Ukraine to assist the Trump re-election effort.

Reps. Adam Schiff, Elijah Cummings, and Eliot Engel, all chairmen of the committees, penned letters Monday to the White House and State Department demanding records related to Trump and Giuliani's alleged attempts to "manipulate the Ukrainian justice system to benefit the President's re-election campaign and target a possible political opponent." They characterized their request as just "the first step in a broad investigation into this matter."

“A growing public record indicates that, for nearly two years, the President and his personal attorney, Rudy Giuliani, appear to have acted outside legitimate law enforcement and diplomatic channels to coerce the Ukrainian government into pursuing two politically-motivated investigations under the guise of anti-corruption activity,” they wrote.

Fox News' Jason Donner and Gregg Re contributed to this report.