-- The senior Justice Department official with ultimate authority over the special counsel's probe of Russia's alleged meddling in the 2016 election has privately acknowledged to colleagues that he may have to recuse himself from the matter, which he took charge of only after Attorney General Jeff Sessions' own recusal, sources tell ABC News.
Rosenstein, who authored an extensive and publicly-released memorandum recommending Comey's firing, raised the possibility of his recusal during a recent meeting with Associate Attorney General Rachel Brand, the Justice Department's new third-in-command, according to sources.
Although Rosenstein appointed a special counsel to lead the federal probe, he still makes the final decisions about resources, personnel and -- if necessary -- any prosecutions.
In the recent meeting with Brand, Rosenstein told her that if he were to recuse himself, she would have to step in and take over those responsibilities. She was sworn-in little more than a month ago.
Potentially complicating matters, Trump posted an exasperated message today on Twitter, dismissing the Russia-related probe as a "witch hunt" and lamenting that he's "being investigated for firing the FBI Director by the man who told me to fire the FBI Director!"
Rosenstein is keenly aware that he could become a potential witness in the investigation.
"I understand there are serious allegations that have been raised," Rosenstein told a Senate panel earlier this week. "I recognize the importance of these questions, and I think that Director Mueller ought to review that and make a determination of whether or not he believes it is within the scope of his investigation."
Sen. Brian Schatz, D-Hawaii, asked Rosenstein specifically whether he might have a conflict of interest if he becomes a witness in the investigation.
"I'm not going to answer hypothetical questions," Rosenstein said. "[But] I am working with career professionals who know these rules and are responsible for enforcing these rules, and I can assure you that we're going to do the right thing, and we're going to defend the integrity of that investigation."
One source said Rosenstein has yet to formally ask career attorneys inside the Justice Department for their opinion on whether he should recuse himself. Any serious contemplation of recusal likely wouldn't happen unless Rosenstein seeks such an opinion.
If Rosenstein were to announce his recusal, it would represent the latest twist in an increasingly unpredictable and dramatic investigation.
Rosenstein took command of the investigation in April, after Sessions announced that he was recusing himself due to his substantial role in Trump's presidential campaign last year. Two months later, at Trump's urging, Rosenstein wrote a letter to the president detailing his belief that Comey should be fired.
Within days, a top Democrat, Sen. Chuck Schumer, D-N.Y., wrote his own letter, insisting that Rosenstein's hard-earned reputation as an "apolitical actor" was "now imperiled" by the deputy attorney general's role in Comey's firing.
Around the same time, Comey orchestrated a series of bombshell news reports laying out portions of one-on-one conversations he allegedly had with Trump, including the infamous conversation in the Oval Office where Trump allegedly told Comey, "I hope you can let this go."
According to Comey, Trump was referring to the FBI's investigation into Mike Flynn, who was fired himself as national security adviser months earlier for allegedly lying to White House officials about his post-election contacts with Russian operatives.
In the wake of those news reports, Rosenstein appointed former FBI Director Robert Mueller to conduct the broad investigation into Russia's alleged meddling in last year's presidential campaign and alleged collusion with Trump associates.
"The public interest requires me to place this investigation under a person who exercises a degree of independence from the normal chain of command," Rosenstein said in his announcement last month.
Rosenstein hasn't spoken with Mueller since, he told lawmakers last week.
But inside his office in recent days, the deputy attorney general has been grappling with what to do about the expanding probe, and seething over news accounts laying out some of its details, according to one source.
Late last night, he issued what many online are calling a "bizarre" statement, condemning recent reports.
"Americans should exercise caution before accepting as true and stories attributed to anonymous 'officials,'" Rosenstein said. "Americans should be skeptical about anonymous allegations. The Department of Justice has a long-established policy to neither confirm nor deny such allegations."
No explanation for the statement was given, but it came just hours after The Washington Post published a story saying Mueller's inquiry is now looking at the finances and business dealings of Jared Kushner, Trump's son-in-law and a key adviser to the president.
The story was attributed to "U.S. officials familiar with the matter."
As for Brand, she previously led the Justice Department's Office of Legal Policy, and she most recently served as a member of the government's Privacy and Civil Liberties Oversight Board. She graduated from Harvard Law School and clerked for Supreme Court Justice Anthony Kennedy, according to the Justice Department.
Sessions recently said she "has proven herself to be a brilliant lawyer."
"She is also a dedicated public servant who is strongly committed to upholding the rule of law and our Constitution," he added.