WASHINGTON — The special counsel investigating possible ties between President Trump’s campaign and Russia’s government has taken over a separate criminal probe involving former Trump campaign chairman Paul Manafort, and may expand his inquiry to investigate the roles of the attorney general and deputy attorney general in the firing of FBI Director James Comey, The Associated Press has learned.

The Justice Department’s criminal investigation into Manafort, who was forced to resign as Trump campaign chairman in August amid questions over his business dealings years ago in Ukraine, predated the 2016 election and the counterintelligence probe that in July began investigating possible collusion between Moscow and associates of Trump.

The move to consolidate the matters, involving allegations of misuse of Ukrainian government funds, indicates that Special Counsel Robert Mueller is assuming a broad mandate in his new role running the sensational investigation.

In an interview Friday with the AP, Deputy Attorney General Rod Rosenstein acknowledged that Mueller could expand his inquiry to include Attorney General Jeff Sessions’ and Rosenstein’s own roles in the decision to fire Comey, who was investigating the Trump campaign. Rosenstein, who appointed Mueller as special counsel to take over the investigation, wrote the memo intended to justify Trump’s decision to fire Comey. Sessions met with Trump and Rosenstein to discuss Trump’s decision to fire him despite Sessions’ pledge not to become involved in the Russia case.

The AP asked Rosenstein specifically whether Mueller’s investigation could expand to include examining Sessions’ role.

“The order is pretty clear,” Rosenstein responded. “It gives him authority for the investigation and anything arising out of that investigation, and so Director Mueller will be responsible in the first instance for determining what he believes falls into that mandate.”

Rosenstein said that if he were to become a subject of Mueller’s investigation, he would recuse himself from any oversight of Mueller. Under Justice Department rules, Mueller is required to seek permission from Rosenstein to investigate additional matters other than ones already specified in the paperwork appointing Mueller.

“I’ve talked with Director Mueller about this,” Rosenstein said. “He’s going to make the appropriate decisions, and if anything that I did winds up being relevant to his investigation then, as Director Mueller and I discussed, if there’s a need from me to recuse I will.”

Mueller, who spent 12 years as FBI director and served under Republican and Democratic presidents, was appointed as special counsel following the May 9 firing of Comey, who is expected to testify for the first time next week before the Senate.

Mueller’s assignment, detailed in a one-page order signed by Rosenstein, covers the federal investigation into possible links between Russia and associates of the Trump campaign but also “any matters that arose or may arise directly” from the probe. It would extend to any allegations of perjury, witness intimidation or obstruction of justice uncovered during the course of the probe.