(CNN) House Judiciary Chairman Jerry Nadler on Monday announced a sweeping investigation into President Donald Trump's campaign, businesses, transition and administration, a probe that would lay the groundwork for Democrats if they choose to pursue impeachment proceedings against the President.

The Judiciary Committee on Monday sent letters to 81 people and entities -- including the White House, the Justice Department, senior campaign officials, Trump Organization officials and the President's sons — marking the start of a broad investigation that will tackle questions including possible corruption, obstruction of justice, hush-money payments to women, collusion with Russia and allegations of the President abusing his office and using it for personal gain.

They are demanding responses within two weeks.

The requests outline a sprawling investigation, seeking documents and communications on issues that include FBI Director James Comey's firing, possible pardons offered to Trump officials, Trump's finances and foreign governments, "catch-and-kill" payments involving the National Enquirer's parent company and Trump, Trump campaign contacts with Russians and WikiLeaks and communications between Trump and Russian President Vladimir Putin.

The committee's investigation comes amid the anticipated conclusion of special counsel Robert Mueller's investigation into possible collusion and obstruction of justice, signaling the committee is likely to retread ground that federal prosecutors have already pursued. Many of the same witnesses that the Judiciary Committee is now requesting information from have already spoken to Mueller's prosecutors and the grand jury.

The wide net cast by the committee also signals that the Democratic-led investigations are likely to stretch on for months, with multiple committees seeking information from senior officials in the White House, the Trump campaign and the Trump Organization.

The evidence gathered in the investigation would be the basis of a possible impeachment proceeding, which the Judiciary Committee would lead, though Nadler has said it's too soon to be discussing impeachment.

"We do not now have the evidence all sorted out and everything to do an impeachment," Nadler said in an interview on ABC's "This Week" on Sunday. "Before you impeach somebody, you have to persuade the American public that it ought to happen."

But Nadler also said that it was "very clear" the President had obstructed justice.

"It's very clear — 1,100 times he referred to the Mueller investigation as a witch hunt, he tried to -- he fired -- he tried to protect (former national security adviser Michael) Flynn from being investigated by the FBI," Nadler said. "He fired (former FBI Director James) Comey in order to stop the Russian thing, as he told NBC News. ... He's intimidated witnesses, in public."

Republicans responded to the new investigation by accusing Democrats of launching a fishing expedition.

"We don't even know what the Mueller report says, but Democrats are already hedging their bets" Georgia Rep. Doug Collins, the top Republican on the Judiciary Committee, said in a statement. "After recklessly prejudging the president for obstruction, Chairman Nadler is pursuing evidence to back up his conclusion because, as he admits, 'we don't have the facts yet.'"

White House press secretary Sarah Sanders echoed that criticism in a statement Monday night.

"Today, Chairman Nadler opened up a disgraceful and abusive investigation into tired, false allegations already investigated by the Special Counsel and committees in both Chambers of Congress," Sanders said. "Chairman Nadler and his fellow Democrats have embarked on this fishing expedition because they are terrified that their two-year false narrative of 'Russia collusion' is crumbling. Their intimidation and abuse of American citizens is shameful."

She added, "Democrats are harassing the President to distract from their radical agenda of making America a socialist country, killing babies after they're born, and pushing a 'green new deal' that would destroy jobs and bankrupt America. The American people deserve a Congress that works with the President to address serious issues like immigration, healthcare, and infrastructure. The Democrats are more interested in pathetic political games and catering to a radical, leftist base than on producing results for our citizens. The Democrats are not after the truth, they are after the President."

Letters first step in broad probe

A Judiciary Committee counsel said that the letters are intended to begin collecting a large trove of evidence that the committee would comb through and then decide who they should bring in to testify.

The counsel said that the committee had spoken about its request with Mueller's team and the US Attorney's office for the Southern District of New York, which has probed the Trump Organization and the Trump Inaugural Committee. Both signed off on the committee's document request, according to the committee's counsel.

Some of the witnesses, particularly those in the White House, could also fight the committee's request for information, citing executive privilege. The committee counsel acknowledged a subpoena fight could be possible with some requests.

Subpoenas might follow, the counsel said, but they will try to negotiate first. Hearings could follow the document requests with some of the officials in the coming weeks.

The White House and the Justice Department acknowledged the letters they received on Monday.

"The House Judiciary Committee's letter has been received by the White House. The Counsel's Office and relevant White House officials will review it and respond at the appropriate time," White House press secretary Sarah Sanders said in a statement.

Asked about the request on Monday, Trump told reporters, "I cooperate all the time with everybody."

"You know the beautiful thing: no collusion," Trump said during a photo opportunity with the champion North Dakota State Bison football team. "It is all a hoax. You're going to learn about that as you grow older. It's a political hoax. There's no collusion."

House Speaker Nancy Pelosi told reporters at an event in Fort Worth, Texas, that "to do anything less would be delinquent in our duties."

"I think what they're doing is exercising their constitutional responsibility for oversight," said Pelosi.

From foreign contacts to hush-money payments

The Democratic-led committee is seeking a range of documents that span the gamut -- from details about contacts with foreign contacts to hush-money payments to silence affairs, which Trump had denied.

Among the people listed in the request for documents include some of Trump's closest associates and family members, including his two sons -- Eric Trump and Donald Trump Jr., son-in-law Jared Kushner, his campaign manager Brad Parscale, former aides Hope Hicks and Don McGahn and longtime employees of the Trump Organization like chief financial officer Allen Weisselberg, and Rhona Graff, a longtime gatekeeper to Trump.

In addition, Nadler is sending letters and demanding documents from David Pecker, the head of the parent company of the National Enquirer, which engaged in a "catch-and-kill" scheme to keep a story quiet about Trump's alleged affair with model Karen McDougal. Nadler wants all documents tied to "any narrative, personal account, documentation, recording, or photograph" tied to Trump from Pecker's company since 2015.

The committee is seeking information about Trump's businesses and foreign governments potentially violating the constitutional ban on presidents accepting payments from government entities, known as the emoluments clause. They are asking the Trump Organization to provide information on "any foreign government discussing, offering, or providing, or being solicited to discuss, offer, or provide, any present or emolument of any kind" after Trump was elected President.

The panel wants documents from a number of officials tied to questions concerning obstruction of justice. For example, Nadler has asked for any documents related to conversations between Trump and McGahn about Flynn's talks with during the transition with then-Russian ambassador to the US Sergey Kislyak, in which Flynn lied to the FBI about discussing sanctions, as well as communications about Flynn's dismissal from the White House. The committee is also seeking from administration officials communications about Comey's firing, then-Attorney General Jeff Sessions' recusal and the "actual or possible resignation or termination" of Sessions, Mueller and Deputy Attorney General Rod Rosenstein.

The letters to two former White House officials, Hicks and Sean Spicer, included a request for personal notes: Hicks was asked about "any personal or work diary, journal or other book," and Spicer was queried about a "personal or work notebook."

Multiple committees seek same Trump officials

The document requests also appear to cover ground already under investigation by other congressional committees and by federal prosecutors.

One example: the committee is demanding a wide range of documents from former Trump attorney Michael Cohen tied to the Trump Organization's efforts to build a Trump Tower Moscow project, a matter that is a part of several investigations. But it also asks Cohen to disclose any discussions he had about pardons with the Trump administration -- something Democrats have asked several witnesses, seeking details about any pardon discussions involving former Trump campaign chairman Paul Manafort and Flynn. And the committee is asking questions about the preparation of Cohen's 2017 congressional testimony in which he admitted to lying.

The committee is also seeking information tied to questions surrounding collusion, including the June 2016 Trump Tower meeting with Russian lawyer promising "dirt," contacts with Russians during the campaign and contacts with WikiLeaks.

Other congressional committees are interested in the same officials, too, creating a possible environment where Democratic-led panels are fighting a turf war to get witnesses before them. For instance, after Cohen's testimony last week, both the House Oversight and Intelligence committees indicated they wanted to speak to Weisselberg, who is on the Judiciary Committee's list as well.

The Department of Justice and the White House also face scrutiny from Nadler. From the White House, Nadler wants a swath of information tied to Russia demanding the White House provide information about contacts with Comey before he was fired as FBI director, details about the firing of Jeff Sessions as attorney general and documents about misleading statements given to the press in 2017 when it was first revealed that Trump Jr. met with Russians during the 2016 campaign.

This story has been updated with additional developments Monday.