Rachel Brand, the No. 3 official at the Department of Justice, is resigning after just nine months on the job — a decision with big ramifications for special counsel Robert Mueller’s investigations.

Here’s why: Deputy Attorney General Rod Rosenstein is currently in charge of overseeing the Mueller probe. Rosenstein has said that he won’t fire Mueller without good cause.

But if Trump were to fire Rosenstein, or if he were to recuse himself from the investigation or quit outright, the responsibility for overseeing the probe would go to the next in line: Associate Attorney General Rachel Brand.

Which means that whoever Trump picks to replace Brand could potentially end up in charge of the Mueller investigation. Technically, the next in line is Solicitor General Noel Francisco, who is now serving in Brand’s role in an acting capacity. But legal experts told me that Trump has the authority to name anyone he wants to replace Brand.

And here’s the scary thing: That person might follow Trump’s order to dismiss the special counsel.

That can only happen if Rosenstein no longer oversees Mueller — and that’s still a distinct possibility for three reasons.

First, Rosenstein could recuse himself from overseeing Mueller because he had a hand in firing former FBI Director James Comey. Mueller became the special counsel because Trump may have let go Comey go in order to obstruct the Russia investigation. So if Rosenstein recuses himself — legal experts, like Jack Goldsmith at Lawfare think he should — then Mueller’s boss becomes whomever Trump may soon name.

Second, Trump could simply fire Rosenstein — and there’s reason to think he might. Trump allies expected last week’s release of the memo from Rep. Devin Nunes would prompt Rosenstein’s dismissal. Trump has consistently made his displeasure with Rosenstein known, at one point claiming he’s “a Democrat” even though Rosenstein is a lifelong Republican.

And finally, Rosenstein could resign if Trump ordered him to fire Mueller. Rosenstein has reiterated time and time again that he has yet to see any reason to fire Mueller. So if Trump does ask Rosenstein to let Mueller go — and Rosenstein declines — Trump could fire Rosenstein. And so, again, Trump’s hand-picked successor would oversee Mueller — and then possibly fire him.

It’s worth noting that the White House continues to say Trump has no plans to fire Mueller. The president even said he expects Mueller to treat him “fairly.” But that won’t stop legal experts, like former top Justice Department spokesperson Matthew Miller, from worrying who the administration will choose to replace Brand.

Who the administration makes acting Associate AG is a critical thing to watch. If Rosenstein has to recuse (and I don't get how he hasn't yet), that person is suddenly Mueller's boss. — Matthew Miller (@matthewamiller) February 9, 2018

Why is Brand leaving?

According to Adam Goldman of the New York Times, Brand took a job as the global governance director for Walmart. Laura Jarret at CNN reported that a friend of Brand said that it was a job you “don’t turn down.”

But there’s a bigger context to her resignation.

In recent days, Trump has escalated his war against federal law enforcement. For example, on Wednesday Trump said that newly released texts from FBI officials were a “bombshell” because they allegedly showed corruption within the bureau. However, there is currently no evidence of widespread corruption within the bureau to depose Trump.

Trump’s broadside fits into a larger pattern. He consistently attacks top law enforcement agents because they won’t help him contain Mueller’s probe. He lambastes Attorney General Jeff Sessions for recusing himself from from overseeing the Mueller investigation, and he criticizes Rosenstein for not halting Mueller’s progress.

Trump appointed both Sessions and Rosenstein to their posts, and yet is still angry with them. That’s an uncomfortable atmosphere for any official at the Department of Justice.