WASHINGTON — Deputy Attorney General Rod Rosenstein today named a onetime lawyer on Sen. John McCain’s 2008 presidential campaign to serve as his right-hand man on overseeing the Russia investigation.

Ed O’Callaghan, who has been serving as the principal deputy assistant attorney general in the National Security Division, is moving over to be acting principal associate deputy attorney general. He’ll replace Robert Hur, who succeeds Rosenstein as the U.S. Attorney for Maryland.

O’Callaghan served as acting assistant attorney general for the National Security Division while waiting for the confirmation of Assistant Attorney General John Demers.

O’Callaghan was an assistant U.S. Attorney for the Southern District of New York from 1999 to 2008 before leaving to join the McCain campaign’s “truth squad.” He spent time in private practice, specializing in “defending financial institutions, public companies, asset management firms, and individuals in international and domestic regulatory investigations and criminal prosecutions — these cases involved securities fraud, bank fraud, money laundering, RICO, and corruption, among other things,” the Justice Department said, before returning to DOJ in 2017.

“Edward O’Callaghan has served the Department of Justice with distinction, excelling as a prosecutor in the Southern District of New York and most recently as the Principal Deputy Assistant Attorney General in the National Security Division. His experiences in a variety of roles throughout the Department will be invaluable as we work to protect our national security, reduce violent crime, and promote the rule of law,” Rosenstein said in a statement.

He also thanked Hur for serving as the principal associate deputy attorney general, as “his counsel was invaluable over the past ten months.”

In response to a dismissal motion from former Trump campaign chairman Paul Manafort, special counsel Robert Mueller late Monday filed a 282-page opposition response that includes a heavily redacted memo from Rosenstein, dated Aug. 2, 2017, elaborating as it relates to certain individuals on the scope of the investigation authorized by Rosenstein upon appointment of the special counsel on May 17, 2017.

The mostly classified memo blocks out copy equivalent to about a page, noting the May appointment order “was worded categorically in order to permit its public release without confirming specific investigations involving specific individuals” and including the description of the allegations that “were within the scope of the Investigation at the time of your appointment are are within the scope of the order.”

The only individual allegations not redacted in the filing are those against Manafort: that he “committed a crime or crimes by colluding with Russian government officials with respect to the Russian government’s efforts to interfere with the 2016 election for President of the United States, in violation of United States law,” and that he “committed a crime or crimes arising out of payments he received from the Ukrainian government before and during the tenure of President Viktor Yanukovych.”

Sen. Richard Blumenthal (D-Conn.), a member of the Judiciary Committee, told CNN today that he believes “as the special counsel comes closer and closer by the day to the president of the United States, the threat to not only Rod Rosenstein, but the special counsel, will mount.”

“That’s the reason that I asked the potential successors to Rod Rosenstein to pledge that they would permit Robert Mueller to proceed with his investigation without political interference, would not fire him, would not restrict his budget or the scope of his investigation, because Rod Rosenstein’s mandate to the special counsel is profoundly important,” Blumenthal said, calling the memo in Mueller’s court filing “so significant because it indicates that the deputy attorney general has given that mandate to Robert Mueller and should be supported.”

“And that’s why we have sponsored legislation that would protect the special counsel and why now, more urgently than ever before, that protection is more vitally necessary,” he added. “And I’m going to be reaching out to my Republican colleagues, because they have an obligation to stand up and speak out, especially now.”

Bipartisan legislation to prevent President Trump from firing his way through the DOJ until he finds someone to fire Mueller has been tabled as Republican supporters of the Mueller probe say they don’t think the congressional protection for the special counsel is necessary.