The deputy attorney general, who's been in law enforcement for close to three decades, is back in the news after the President tweeted Friday morning that he is being investigated for his role in firing former FBI Director James Comey and seemed to accuse Rosenstein of overseeing a "witch hunt" against him.
Mueller has hired 13 new lawyers to help him handle his investigation into whether Trump obstructed justice and if members of his presidential campaign colluded with Russian Federation to influence the outcome of the 2016 election. But Comey has testified under oath that in a private meeting, Trump raised the investigation of fired national security adviser Michael Flynn - part of the larger Russian Federation probe - and said, "I hope you can see your way clear to letting this go, to letting Flynn go". "Witch Hunt", the president wrote in his tweet.
Trump wrote that the investigation has not "been able to show any proof", an allegation that he assessed with one of his signature Twitter catchphrases: "Sad!"
Trump's 9:07 a.m. tweet appeared to be principally directed at Deputy Attorney General Rod Rosenstein, the number-two official at the Justice Department who authored a memo justifying Comey's firing.
As part of his probe into possible obstruction, Mueller has requested interviews with senior intelligence officials about their conversations with Trump, a former senior intelligence official with knowledge of the discussions confirmed to NBC News.
Press Secretary Sean Spicer recently confirmed President Trump's tweets are in fact official statements.
Comey said he believed Trump's advice to be a direction and thus felt uncomfortable by it.
Meanwhile, California Senator Dianne Feinstein expressed concerned that Trump will attempt to fire not only Special Counsel Mueller, who is now investigating him for possible obstruction of justice, but also Rosenstein.
The memo to former transition team members on Thursday also seeks specific information on five people, the Times reported, They include Paul Manafort, Trump's former campaign manager; Rick Gates, Manafort's business partner; Carter Page, a former foreign policy adviser; former national security adviser Michael Flynn; and Roger J. Stone Jr., an informal adviser to Mr. Trump.
"Americans should be skeptical about anonymous allegations", Rosenstein said.
The president has denied that he has any nefarious ties to Russian Federation and has also disputed that he's attempted to block the investigation into his campaign's possible role in Russia's election-related hacking.
Through a spokesman, Trump's personal attorney, Marc Kasowitz, blasted the Post's report, though he stopped short of denying it.