WASHINGTON (AP) — Attorney General William Barr, one of President Donald Trump’s staunchest allies, is resigning amid lingering tension with the president over the president’s baseless claims of election fraud and the investigation into President-elect Joe Biden’s son.

Barr went Monday to the White House, where Trump said the attorney general submitted his letter of resignation. “As per letter, Bill will be leaving just before Christmas to spend the holidays with his family,” Trump tweeted.

Trump has publicly expressed his anger about Barr’s statement to The Associated Press earlier this month that the Justice Department had found no widespread election fraud that would change the outcome of the election. Trump has also been angry that the Justice Department did not publicly announce it was investigating Hunter Biden ahead of the election, despite department policy against such a pronouncement.

Barr in his resignation letter said he updated Trump Monday on the department’s “review of voter fraud allegations in the 2020 election and how these allegations will continue to be pursued.” He added that his last day on the job would be Dec. 23.

Trump said Deputy Attorney General Jeff Rosen, whom he labeled “an outstanding person,” will become Acting Attorney General.