The Justice Department is appointing former FBI Director Robert Mueller as a special counsel to oversee the growing probe into Russian meddling in the 2016 election and possible ties to associates of President Trump.

“In my capacity as acting Attorney General, I determined that it is in the public interest for me to exercise my authority and appoint a Special Counsel to assume responsibility for this matter,” Deputy Attorney General Rod Rosenstein said in a statement.

The appointment of Mueller, who is widely respected on both sides of the aisle, comes after growing outcry, mostly from Democrats, amid fallout of President Trump’s firing of FBI Director James Comey last week. While the White House initially insisted the dismissal was precipitated by Comey’s mishandling of the investigation into Democratic presidential nominee Hillary Clinton’s emails, outlined by Rosenstein in a memo, Trump later told NBC’s Lester Holt that the Russia investigation factored into his decision.

Several reports allege that Trump asked Comey to scuttle an investigation into former national security adviser Michael Flynn the day after Flynn resigned. Flynn stepped down after reports he had misled Vice President Pence about his conversations with the Russian ambassador. The White House denies that Trump made the request to shut down the probe.

Mueller, who preceded Comey at the FBI, had a 12-year stint at the agency after being unanimously confirmed by the Senate in 2001, just the week before the Sept. 11 terrorist attacks. His tenure leading the bureau was defined by what he did to adapt to the new threats posed to America by terrorism, and he was asked by then-President Barack Obama to stay on beyond the typical 10-year term for two additional years, which Congress approved.

Since retiring from the FBI in 2013, he has been working as a partner for the law firm WilmerHale, which confirmed Thursday night that Mueller had resigned from the firm immediately upon his appointment to the new post.