President Trump on Friday approved the release of a controversial memo alleging that the FBI and Department of Justice abused their surveillance authority to target Trump campaign adviser Carter Page.

The Republican majority on the House Intelligence Committee, which wrote the memo, made it public within minutes. Read the memo here.

The White House made no changes to the memo, spokesman Raj Shah said, and declassified the document "in full." The president repeated his charges of bias by investigators after signing off on the memo's release.

"I think it’s a disgrace,” Trump told reporters, and people should be “ashamed.”

"A lot of people should be ashamed of themselves," he said. Trump had tweeted earlier Friday that "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."

Democrats have denounced the memo as a blatant attempt by Trump and House Republicans to discredit special counsel Robert Mueller's investigation of Russian meddling in the 2016 election.

The memo alleges that top law enforcement officials relied on an unsubstantiated dossier compiled by former British spy Christopher Steele to get a warrant to conduct surveillance of Page. The dossier was funded by the Democratic National Committee and the Hillary Clinton campaign.

In a statement Friday, Page said: “The brave and assiduous oversight by congressional leaders in discovering this unprecedented abuse of process represents giant, historic leap in the repair of American democracy."

Among those who certified the application for the initial warrant and subsequent renewals were: former FBI Director James Comey, whom Trump fired last year; former Deputy Director Andrew McCabe, who just retired; and Deputy Attorney General Rod Rosenstein, who is overseeing Mueller's investigation.

Others included former Deputy Attorney General Sally Yates, who was also fired by Trump last year; and then-Acting Deputy Attorney General Dana Boente. In January, Boente became the new general counsel for the FBI.

Rosenstein is the only top official who hasn't been fired or taken a new job. Democratic leaders from the House and Senate sent a letter to Trump on Friday afternoon warning him not to use the partisan memo as a basis to fire Rosenstein or Mueller.

"We are alarmed by reports that you may intend to use this misleading document as a pretext to fire Deputy Attorney General Rod Rosenstein, in an effort to corruptly influence or impede Special Counsel Bob Mueller’s investigation," said the letter, which was signed by House Minority Leader Nancy Pelosi, D-Calif., Senate Majority Leader Chuck Schumer, D-N.Y., and eight others.

"We write to inform you that we would consider such an unwarranted action as an attempt to obstruct justice in the Russia investigation," the letter says. "Firing Rod Rosenstein, DOJ Leadership, or Bob Mueller could result in a constitutional crisis of the kind not seen since the Saturday Night Massacre."

The Saturday Night Massacre is a reference to former president Richard Nixon's firing of Watergate Special Prosecutor Archibald Cox, which led to the resignations of Attorney General Elliot Richardson and Deputy Attorney General William Ruckelshaus. Nixon ultimately resigned rather than be impeached.

The memo released Friday was written by the Intelligence Committee's Republican staff, at the direction of Chairman Devin Nunes, R-Calif.

The committee sent the memo to the White House on Monday night, giving Trump time to decide whether to block its release.

The release puts Trump at odds with FBI Director Christopher Wray and Rosenstein, who had urged the White House not to release it for fear that it could reveal classified information and jeopardize national security.

Democrats on the committee have complained that the memo cherry-picks information designed to discredit the investigation into Russia's election interference and possible collusion with Trump associates. Mueller's probe is also looking into possible obstruction of justice by Trump in his efforts to limit the investigation. Nunes has been a close ally of Trump, and worked on the Trump transition after the election.

"The premise of the Nunes memo is that the FBI and DOJ corruptly sought a FISA (Foreign Intelligence Surveillance Act) warrant on a former Trump campaign foreign policy adviser, Carter Page, and deliberately misled the court as part of a systematic abuse of the FISA process," said Rep. Adam Schiff of California, the committee's senior Democrat. "None of this is true. The FBI had good reason to be concerned about Carter Page and would have been derelict in its responsibility to protect the country had it not sought a FISA warrant."

Schiff said the investigation of Page did not arise from the infamous dossier, despite Republican claims to the contrary. "The investigation would persist on the basis of wholly independent evidence had Christopher Steele never entered the picture," Schiff said.

The FBI expressed "grave concerns" Wednesday about the memo's release, suggesting it is inaccurate.

"The FBI was provided a limited opportunity to review this memo the day before the committee voted to release it," the bureau said in a statement. "As expressed during our initial review, we have grave concerns about material omissions of fact that fundamentally impact the memo’s accuracy."

Nunes said Friday that his committee "has discovered serious violations of the public trust, and the American people have a right to know when officials in crucial institutions are abusing their authority for political purposes."

"Our intelligence and law enforcement agencies exist to defend the American people, not to be exploited to target one group on behalf of another," Nunes said. "It is my hope that the Committee’s actions will shine a light on this alarming series of events so we can make reforms that allow the American people to have full faith and confidence in their governing institutions."

FBI agents defended the bureau after the memo's release.

"The men and women of the FBI put their lives on the line every day in the fight against terrorists and criminals because of their dedication to our country and the Constitution," said Tom O'Connor, president of the FBI Agents Association. "The American people should know that they continue to be well-served by the world’s pre-eminent law enforcement agency. FBI special agents have not, and will not, allow partisan politics to distract us from our solemn commitment to our mission."

The committee's Republican majority voted Monday night to declassify and release the four-page memo, while Democrats opposed it. Republicans also blocked the release of a rebuttal memo written by Democrats.

Contributing: David Jackson, Kevin Johnson