United States Attorney General Jeff Sessions has resigned.

Sessions announced his resignation in a letter to President Donald Trump on Wednesday. He wrote, “At your request, I am submitting my resignation.”

Trump announced on Twitter that Session’s chief of staff, Matthew Whitaker, a former United States attorney from Iowa will become acting attorney general. Trump thanked Sessions for his service and said “a permanent replacement will be nominated at a later date.”

The resignation brings to an end a difficult relationship between the two men.

Trump strongly criticized Sessions’ decision to step aside from the investigation into Russian interference in the 2016 presidential election. Sessions did so after it was reported that he met with Russian officials before the election. Sessions had also served on Trump’s election campaign team.

Sessions’ admission angered Trump who said he never would have nominated the former Alabama senator if he knew he would have stepped aside.

Sessions decided to step aside in March of 2017 and left Deputy Attorney General Rod Rosenstein in charge of the investigation. Rosenstein then appointed special counsel Robert Mueller who has investigated a wide number of possible crimes including failure to pay taxes and lying to investigators.

Trump has criticized the investigation as a “witch hunt.”

What will happen to Mueller investigation?

The Justice Department did not announce a departure for Deputy Attorney General Rod Rosenstein. However, spokeswoman Sarah Flores said Whitaker would be “in charge of all matters under the purview of the Department of Justice.”

Whitaker once discussed a situation in which Trump could fire Sessions and then appoint an acting attorney general. The appointee could then reduce funding for Mueller’s investigation.

Whitaker told CNN in July 2017, “So I could see a scenario where Jeff Sessions is replaced with a recess appointment and that attorney general doesn’t fire Bob Mueller, but he just reduces his budget to so low that his investigation grinds to almost a halt.”

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

Senator Mark Warner is the ranking Democrat on the Senate Intelligence Committee. Warner wrote on Twitter, “Given Mr. Whitaker’s public comments on the Special Counsel’s investigation and the President’s obvious self-interest in appointing him to the Acting AG role, Mr. Whitaker should recuse himself.”

He added, “While the President may have the authority to replace the Attorney General, this must not be the first step in an attempt to impede, obstruct or end the Mueller investigation.”

Several Republican Party lawmakers had warned Trump not to dismiss Sessions. However, support for the attorney general seemed to decrease over this year.

Sessions served for 20 years in the U.S. Senate before taking the office of the nation’s top law enforcement official.

I’m Pete Musto.