Jeff Sessions has resigned as attorney general and will be replaced by Matthew Whitaker, President Trump announced Wednesday afternoon.

The Associated Press reports that Sessions submitted his resignation in a letter to Trump. He resigned at the president's request, according to the AP.

Sessions has served as attorney general since the early days of Trump's administration.

Whitaker is currently Sessions's chief of staff.

Sessions had recused himself from special counsel Robert Mueller's probe into possible coordination between Trump's presidential campaign and Russia. Deputy Attorney General Rod Rosenstein was placed in charge of the probe. It is unclear who will oversee it going forward.

Trump and Sessions had a falling out after the attorney general recused himself from Mueller's investigation. The president has repeatedly belittled Sessions in public and expressed regret about appointing him.

Last year, Whitaker wrote an op-ed for CNN that accused Mueller's investigation of going too far.

Senate Minority Leader Charles Schumer has already called on Whitaker to recuse himself from the investigation.

New York City Rep. Jerrold Nadler, who is currently the ranking Democratic member of the House Judiciary Committee (and could be the next chairman of the committee with Democrats projected to take control of the House), questioned the president's move on Twitter and said that "we will be holding people accountable."

Schumer said it is "paramount'' that the investigation of special counsel Robert Mueller be protected by Trump's new attorney general.

Schumer said he found the timing of Sessions's departure "very suspect.'' He said it would spark a "constitutional crisis'' if Trump forced out Sessions as a "prelude'' to ending or limiting Mueller's investigation.