President Trump tweeted Monday that Attorney General Bill Barr will resign from his post before Christmas, moments after the Electoral College affirmed President-elect Joe Biden's election victory.

Why it matters: Tensions between Trump and Barr had already been running high, and revelations in the Wall Street Journal that Barr had worked "for months" during the campaign to conceal a federal investigation of Hunter Biden further enraged the president.

Behind the scenes: Prior to the Hunter Biden report, Trump for weeks had privately discussed replacing Barr with somebody more willing to do his bidding.

Barr's comments to the AP earlier this month, in which he undercut Trump's claims of a "rigged election" by saying the Justice Department has not found evidence of widespread fraud that would change the outcome, sent the president into a rage.

Additionally, Trump had grown frustrated over the delays in the release of the so-called Durham report, which he hopes will contain bombshell revelations about the Obama administration's handling of the Trump-Russia investigation.

Barr resigned without Trump having to request his resignation, according to a source familiar.

Speculation that Trump would fire Barr temporarily subsided after the attorney general visited the White House the day that the AP interview was published. But as Axios reported this weekend, Trump began re-exploring options for replacing Barr after the Hunter Biden story broke.

Trump was privately venting about Barr on Friday with confidants, including Rep. Jim Jordan (R-Ohio), sources familiar with the discussions tell Axios.

And the president tweeted on Saturday morning: "Why didn't Bill Barr reveal the truth to the public, before the Election, about Hunter Biden[?]"

Between the lines: Trump has a history of dropping his own announcements at moments when cable news is running stories that he hates — in this instance, the Electoral College affirming Biden's victory. This looks like another example of the president tweeting his way out of chyrons.

What's next: Trump said that Barr will be replaced by Deputy Attorney General Jeff Rosen, who will serve in an acting capacity.

The big picture: Barr, the second Senate-confirmed attorney general appointed by Trump, has been a fierce critic of the Russia probe and one of the most loyal members of the president's Cabinet — filling a role vacated by Jeff Sessions, who was unceremoniously fired by Trump for failing to stop the Mueller investigation.

He has frequently been a target of criticism by Democrats who claim he has politicized the Justice Department by intervening in cases involving the president's allies.

But like many top Trump officials, even Barr has failed to go far enough to satisfy Trump's desires.

Read Barr's resignation letter.