House Republicans on Friday released a bitterly disputed, formerly highly classified memo that they say shows surveillance abuses in the early stages of the FBI's investigation into the Trump election campaign and Russia.

President Trump, who championed release of the document over the fierce objections of his own Justice Department, declared the memo shows a "lot of people should be ashamed of themselves."

The memo, prepared by Republicans on the House intelligence committee, asserts that the FBI relied excessively on opposition research funded by Democrats in seeking a warrant to monitor the communications of a Trump campaign associate. It says federal authorities concealed the full details of who was paying for the information.

Mr. Trump has been telling confidants that he believed the document would validate his concerns that the FBI and Justice Department conspired against him. But the FBI says the four-page document is inaccurate and stripped of critical context.

Democrats say the memo, which makes public material that is ordinarily considered among some of the most tightly held national security information, cherry-picks Republican talking points in an effort to smear law enforcement.

Rep. Adam Schiff of California, the committee's top Democrat, said that the Republican document "mischaracterizes highly sensitive classified information" and that "the selective release and politicization of classified information sets a terrible precedent and will do long-term damage to the intelligence community and our law enforcement agencies."

The memo had been classified since it deals with warrants obtained from the secret Foreign Intelligence Surveillance Court. The White House declassified it on Friday and sent it to the intelligence committee chairman, Republican Rep. Devin Nunes of California, for immediate release.

The disclosure of the document is likely to further escalate an intra-government conflict that has split the president and his hand-picked law enforcement leaders.

It also comes amid an ongoing effort by Trump and congressional Republicans to discredit an investigation by special counsel Robert Mueller that focuses not only on whether the campaign coordinated with Russia but also on whether the president sought to obstruct justice. Republicans seized on the allegations in the memo to argue that the FBI's investigation was politically tainted from the start.

That argument takes aim at an FBI counterintelligence investigation started many months before Mr. Mueller was appointed as special counsel, though he inherited the probe in May.

Trump, who lashed out anew at the FBI and Justice Department ahead of the document's release, refused to express confidence in Deputy Attorney General Rod Rosenstein, who appointed Mueller and is mentioned by name in the memo.

Does Trump have confidence in Mr. Rosenstein? he was asked. "You figure that one out," he retorted.

Of the memo, Trump said, "I think it's a disgrace. What's going on in this country, I think it's a disgrace."

Earlier in the day, he tweeted, "The top Leadership and Investigators of the FBI and the Justice Department have politicized the sacred investigative process in favor of Democrats and against Republicans – something which would have been unthinkable just a short time ago. Rank & File are great people."

The memo offered the first government confirmation that the FBI in October 2016 obtained a secret warrant from the Foreign Intelligence Surveillance Court to monitor a Trump campaign associate, Carter Page, on the basis that the FBI believed he might be an agent of a foreign power – in this case, Russia. That warrant was reauthorized multiple times, including by Rosenstein.

The memo asserts that opposition research conducted by a former British spy, Christopher Steele, "formed an essential part" of the initial application to receive the warrant. It's unclear how much or what information that Mr. Steele collected was included in the application. Steele's research was compiled into a dossier of salacious allegations involving Trump and Russia. It's unclear how much has been corroborated by the FBI.

Regardless, the FBI routinely relies on multiple sources of information when it obtains surveillance warrants, and that information oftentimes is not verified at the time agents make their applications.

Steele's opposition research effort was initially funded by the conservative Washington Free Beacon. It was later picked up by the Hillary Clinton presidential campaign through a Washington law firm.

In a statement, Page, who served as a foreign policy adviser and came on the FBI radar in 2013 as part of a separate counterintelligence probe, said, "The brave and assiduous oversight by Congressional leaders in discovering this unprecedented abuse of process represents a giant, historic leap in the repair of America's democracy."

The memo release, and Trump's tweet, escalates a clash with the man he picked to lead the FBI, Christopher Wray, after firing James Comey as agency director. It also seemed at odds with House Speaker Paul Ryan who said a day earlier "this memo is not an indictment of the FBI or the Department of Justice."

FBI officials, including Mr. Wray, have also made direct appeals to the White House, warning that the declassification and release could set a dangerous precedent.

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Mr. Comey weighed in on Twitter as well, saying: "All should appreciate the FBI speaking up. I wish more of our leaders would. But take heart: American history shows that, in the long run, weasels and liars never hold the field, so long as good people stand up. Not a lot of schools or streets named for Joe McCarthy."

This story was reported by The Associated Press.