Sen. Richard Blumenthal (D-Conn.) compared House Intelligence Committee Chairman Devin Nunes Devin Gerald NunesSunday shows preview: With less than two months to go, race for the White House heats up Sunday shows preview: Republicans gear up for national convention, USPS debate continues in Washington Sunday shows preview: White House, congressional Democrats unable to breach stalemate over coronavirus relief MORE's (R-Calif.) move to make a memo on surveillance at the Department of Justice (DOJ) public to former Sen. Joseph McCarthy's (R-Wis.) aggressive probe of suspected communists in the 1950s.

"The release of this memo is really reminiscent of the darkest days of the McCarthy era, with character assassinations," Blumenthal told CNN's Alisyn Camerota on "New Day."

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"It endangers methods and sources of the intelligence community, and it reflects an effort to distract from the [Robert] Mueller investigation," he continued, referring to the special counsel probing alleged ties between the Trump campaign and Russia's election meddling.

McCarthy claimed numerous Soviet and communist sympathizers had infiltrated the U.S. government during the Cold War.

The House Intelligence Committee voted on Monday to make the GOP-drafted memo public, which alleges abuse of surveillance at the DOJ. President Trump Donald John TrumpHR McMaster says president's policy to withdraw troops from Afghanistan is 'unwise' Cast of 'Parks and Rec' reunite for virtual town hall to address Wisconsin voters Biden says Trump should step down over coronavirus response MORE has to sign off on releasing the document.

Democrats say the memo works to undermine Mueller's probe.

The FBI expressed its concerns on the memo in a rare public statement on Thursday.

"As expressed during our initial review, we have grave concerns about material omissions of fact that fundamentally impact the memo’s accuracy," the FBI said.

The committee's ranking Democrat Rep. Adam Schiff Adam Bennett SchiffOvernight Defense: Top admiral says 'no condition' where US should conduct nuclear test 'at this time' | Intelligence chief says Congress will get some in-person election security briefings Overnight Defense: House to vote on military justice bill spurred by Vanessa Guillén death | Biden courts veterans after Trump's military controversies Intelligence chief says Congress will get some in-person election security briefings MORE (Calif.) on Wednesday claimed that Nunes had shared a "secretly altered" version of the document with Trump.

"Discovered late tonight that Chairman Nunes made material changes to the memo he sent to White House — changes not approved by the Committee. White House, therefore, reviewing a document the Committee has not approved for release." Schiff said in a tweet.

Blumenthal told Camerota changes made to the memo were done without the knowledge of Democrats working on the committee.

"What we know for sure is that they are unauthorized by the minority on the committee. They were made without their knowledge or approval," Blumenthal said.

Trump was expected to announce his decision on whether to release the memo on Friday; however, Schiff's letter could delay that decision.