Who is Matthew Whitaker, the acting U.S. Attorney General?

Whitaker, 48, was Sessions’ chief of staff.

Shortly after the announcement, The Hill reported that Whitaker will now oversee the Russia probe headed by special counsel Robert Mueller, taking the place of Deputy Attorney General Rod Rosenstein.

"The Acting Attorney General is in charge of all matters under the purview of the Department of Justice," Department of Justice spokeswoman Sarah Isgur Flores said in a statement to The Hill.

Before joining Sessions' staff, Whitaker wrote an op-ed for The Hill in August 2017 urging more scrutiny of a meeting between Ukrainian officials and Democrats in the 2016 presidential campaign.

In an op-ed that Whitaker wrote for CNN in August 2017 -- when he was a legal commentator for the cable news network -- he argued that the Mueller probe was coming close to crossing a "red line."

“Mueller has come up to a red line in the Russia 2016 election-meddling investigation that he is dangerously close to crossing,” Whitaker wrote.

Whitaker ran as a Republican for the post of Iowa state treasurer in 2002, but lost to incumbent Democrat Michael Fitzgerald. In 2014 he ran for the U.S. Senate but was eliminated in a campaign that was won by Joni Ernst.

In 2004, he was appointed U.S. Attorney for the Southern District of Iowa by President George W. Bush. He resigned from the position in November 2009 after the confirmation of Nicholas A. Klinefledt, who was appointed by President Barack Obama.

From November 2009 to September 2017, Whitaker was managing partner of Whitaker Hagenow & Gustoff LLP, a law firm in Des Moines, Iowa.

In 2014, Whitaker joined the board of World Patent Marketing, a patent assistance company. He joined Sessions staff after the company was shut down by the Federal Trade Commission for fraud.

Whitaker grew up in Ankeny and played football at Ankeny High School, where he was named to the all-state football team, according to WHO-TV.

He was inducted into the Iowa High School Football Hall of Fame in 2009.

Whitaker attended the University of Iowa, where he graduated with a bachelor's degree in communications studies in 1991, according to his LinkedIn profile. In 1995 he received a master's degree in finance from the university's Tippie College of Business. He earned his Juris Doctor degree the same year.

Whitaker played tight end for the Hawkeyes football team, appearing in the 1991 Rose Bowl, when Iowa lost 46-34 to the University of Washington.