One outstanding investigation is special counsel Robert Mueller's probe into Russian meddling in the 2016 election. Rosenstein oversaw Mueller's probe for more than a year, after former Attorney General Jeff Sessions had recused himself from the matter over his role in President Donald Trump's campaign.
At the time, sources said Rosenstein had wanted to serve about two years and that there was no indication that he was being forced out by the president. Rosenstein had became a frequent target of Trump's on Twitter, with the president re-posting an image of Rosenstein and others behind bars late last year.
In February, the White House named Jeff Rosen, currently the deputy secretary at the Department of Transportation, as Rosenstein's successor.