U.S. President Donald Trump assailed Democratic lawmakers Tuesday for opening a wide-ranging investigation of him and his administration, calling it "a big, fat, fishing expedition in search of a crime."He contended that Democrats in the House of Representatives, who on Monday demanded documents from 81 people and entities linked to his 2016 campaign, his businesses and his two-year tenure as president, "have gone stone cold CRAZY." He said letters looking for information were sent to "innocent people to harass them." On Twitter, he called the House Judiciary Committee investigation "the greatest overreach in the history of our Country. The Dems are obstructing justice and will not get anything done." "PRESIDENTIAL HARASSMENT!" he declared in a final, all-caps broadside. The House panel said it is investigating whether Trump has obstructed justice to thwart probes of him, as well as possible public corruption and abuses of power during his two-year presidency.In announcing the investigation, Judiciary Committee chairman Jerrold Nadler said, "Over the last several years, President Trump has evaded accountability for his near-daily attacks on our basic legal, ethical and constitutional rules and norms. Investigating these threats to the rule of law is an obligation of Congress." Trump has long denied wrongdoing involving his campaign's links to Russia and during his presidency. Asked about the Nadler investigation on Monday, Trump replied, "I cooperate all the time with everybody.... You know the beautiful thing? No collusion. It’s all a hoax."In a statement, White House press secretary Sarah Sanders said the Democrats launched the investigation "because they are terrified that their two-year false narrative of 'Russia collusion' is crumbling. Their intimidation and abuse of American citizens is shameful. 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." She said White House lawyers and "relevant White House officials" would review the Judiciary Committee's demand for documents and "respond at the appropriate time."Aside from the White House, the panel sent its requests for documents to the Justice Department; senior campaign officials; the Trump Organization, the president's global business empire; and his two oldest sons, Donald Trump Jr. and Eric Trump.Nadler said Sunday he believes the president has obstructed justice. He said that Trump's former long-time personal lawyer, Michael Cohen, in his lengthy public testimony to Congress last week, "directly implicated the president in various crimes, both while seeking the office of president and while in the White House." "We don't have the facts yet," Nadler said. "But we're going to initiate proper investigations."The information gathered by the Judiciary Committee, along with that in the yet-to-be-released report by special counsel Robert Mueller's investigation of Trump campaign links to Russia and obstruction allegations, could form the basis of impeachment proceedings against Trump. But Nadler said talk of trying to remove Trump from office is premature."We will act quickly to gather this information, assess the evidence and follow the facts where they lead with full transparency with the American people," he said.Mueller's report could soon be turned over to Attorney General William Barr, but how much of it will be made public is uncertain. Democratic lawmakers have called for its full release, but Barr has said he would only do so to the extent that Justice Department regulations allow.What is certain is that Barr intends to maintain oversight of the probe, unlike his predecessor Jeff Sessions, who recused himself from the Russia probe after it was disclosed he had failed to tell lawmakers during his confirmation hearing that he had two meetings with Russia's former ambassador to Washington, Sergey Kislyak. "Following [Attorney] General Barr's confirmation, senior career ethics officials advised that General Barr should not recuse himself from the special counsel's investigation," the Justice Department said Monday. "Consistent with that advice, General Barr has decided not to recuse."Barr drew scrutiny for a memo he wrote criticizing Mueller's investigation, but said during his confirmation hearings the document should not be taken as a wide-ranging prejudgment of the process.White House bureau chief Steve Herman contributed to this report.