President Trump sits with Attorney General Jeff Sessions during the FBI National Academy graduation ceremony in Quantico, Va. (AP)

This article has been updated.

Twice in the past week, President Trump has offered vague threats against the Justice Department, apparently as a function of his frustration with the ongoing investigation being conducted by special counsel Robert S. Mueller III.

There was Trump’s comment during his phone interview with Fox News’s “Fox and Friends,” during which he said, “I’ve taken the position — and I don’t have to take this position, and maybe I’ll change — that I will not be involved with the Justice Department. I will wait until this is over. It’s a total — it’s all lies, and it’s a horrible thing that’s going on.”

On Wednesday morning, the threat was in a tweet:

The frustration here is apparently frustration both over Deputy Attorney General Rod J. Rosenstein’s dismissal of the threat of impeachment and, perhaps, the department’s rejection of a request from House Republicans for documents pertaining to Mueller’s investigation.

What’s not clear, though, is what “I will have no choice but to use the powers granted to the presidency and get involved” actually means.

Asked by email what Trump might be driving at, Louis Seidman, Carmack Waterhouse Professor of Constitutional Law at Georgetown University, was blunt.

“Frankly, I have no idea,” he replied. He noted, though, that Trump might be speculating about something more significant than simply replacing Attorney General Jeff Sessions.

“Although it would violate norms that have been in place since Watergate,” Seidman wrote, “Trump could simply order Sessions or Rosenstein to do things. Some of these orders might violate existing DOJ [regulations], but he could also order them to repeal the regs. He could then fire them if they refused. Doing these things would impose political costs … but the legal protections against this sort of thing are thin.”

Let’s start with that first point, that Trump could order his officials at Justice to perform certain actions, such as releasing documents or firing Mueller. Trump is Sessions’s boss, just as he is the boss of the heads of the other administrative departments. In recent years, presidents have treated the Justice Department and the attorney general differently, affording them more independence to preserve the integrity of investigations. But that’s a custom, not a law, that stemmed from concerns about Richard Nixon’s handling of Watergate. As Seidman noted, there may be documented regulations preventing Trump from intervening in an action, but those can be revised by Sessions or the attorney general.

For example, a memo written by then-Attorney General Michael B. Mukasey in 2007 dictates that Justice would only inform the White House about criminal or civil cases “only where it is important for the performance of the President’s duties and where appropriate from a law enforcement perspective.” But another memo from Sessions or a successor to Sessions could simply eradicate that guideline.

Trump has already shown a willingness to ignore measures meant to protect independence within the department. Directors of the FBI are given 10-year terms to protect them from political influence. That didn’t keep Trump from removing James B. Comey from that position last May.

“The only restraint here is political,” former White House attorney and Georgetown Law professor Victoria Nourse told VOA News in February, “which is to say, if he were to do those things, the other side would say, ‘Look, this is improper action, and it has to result in censure or some kind of impeachment.’”

More on that in a bit.

Seidman pointed to the Nixon presidency for evidence of possible political costs of firing Sessions or Rosenstein. Before confirming Elliot Richardson as Nixon’s attorney general, the Democrat-led Congress extracted a promise from Richardson that he would not fire the special prosecutor investigating the Watergate break-in. When Nixon demanded he do so anyway, Richardson resigned. Were Trump to fire Sessions or Rosenstein, Seidman argues, Congress might demand that their replacements protect special counsel Robert S. Mueller III’s investigation (or a continuation of that investigation, should Mueller also be ousted). The net effect of that would be to bolster the investigation into Trump, not weaken it.

Trump may be betting, though, on one of two things happening. The first is that he may be assuming that he has the ability to simply replace Sessions or Rosenstein with someone else who’s received Senate confirmation under the terms of the Federal Vacancies Reform Act of 1998. As Georgetown Law professor Paul Butler explained last year, Trump could potentially replace Sessions with anyone else who’s already been confirmed by the Senate (such as a Cabinet member or another senior administration official) — though it may require a legal fight to determine if the act applies after a presidential firing, as opposed to a resignation. (It’s not clear from the regulation.) If Sessions or Rosenstein resigned instead of complying, that issue goes away.

The other thing he may be betting on is the different political environment of the moment. There’s been a lot of discussion about congressional action to protect Mueller’s position, but nothing’s happened. Senate Majority Leader Mitch McConnell (R-Ky.) has expressed his opposition to such a measure, though that’s been predicated on the idea that it’s unnecessary. Nixon faced the opposition party on Capitol Hill. The Republican majority in the Senate is slim, but it’s a majority. Would two Republicans balk at a presidential nominee to defend a Justice Department that the Republican base sees as unfair?

This is the Achilles’ heel to Nourse’s point, as well. Sure, the other side might say that Trump’s interference in the Justice Department has to result in action by Congress — but Democrats don’t control Congress. The question comes down to the willingness of Trump’s own party to take action were he to violate the norms that are in place. If that’s even what Trump might be thinking. The vagueness of his threat seems more like his mention of “tapes” after the Comey firing than anything specific, an effort to express frustration by implying that he might do something dramatic.

More broadly, the reason presidents don’t intervene in Justice Department investigations is to avoid the appearance of political bias. The FBI and the Justice Department are meant to be nonpartisan investigators adhering to strict rules of impartiality. Our government is intended to be one in which its power isn’t leveraged to settle personal grudges or for political advantage, and maintaining trust that this is the case means fighting against even the impression that bias has infected the department’s work.

Trump and his allies would argue that this has already happened, that the investigations targeting him are biased and founded on partisan sentiment and that trust in the department has waned. It’s an argument that’s been effective with his base, even if the evidence for the claims is thin to nonexistent. (The investigation wasn’t a function of the dossier of allegations paid for by attorneys representing the Democratic Party, for example, and it’s led by career Republicans, even if some members of Mueller’s team have supported Democrats.) That trust in the department has waned with his base is, of course, almost entirely a function of Trump and his allies criticizing the department as biased against him.

It’s also possible that Trump is using a North Korea-style strategy, threatening the Justice Department and Mueller in an effort to bring the investigation to a more rapid conclusion. Given that we don’t actually know what he’s threatening, it’s hard to know if that might work.

Update: Lisa Kern Griffin, professor of law at Duke University, also offered her thoughts over email. They are below, lightly edited.

What the President’s tweets mean or portend is anyone’s guess. He appears to be signaling about two notions he favors: presidential control over the Department of Justice generally, including the conduct of individual investigations, and his absolute authority to make personnel decisions.

He’s not quite correct on either count.

While the White House can weigh in through specific channels about policies the Justice Department pursues, it is not supposed to discuss ongoing criminal investigations unless they directly and immediately implicate national security. Nor is the President empowered to dismiss the Special Counsel himself, which is why it’s been pointed out that “getting involved” might precipitate a constitutional crisis.

The temperature has gone up a couple of degrees on the investigations in both the Special Counsel’s Office and the Southern District of New York [into Trump’s attorney Michael Cohen], and the President is expressing some frustration about that and making blustery threats. He likely won’t act on those threats until he calculates that his personal jeopardy is such that the political costs are worth paying. In the meantime, the strategy seems to be to generally discredit the investigation and the law enforcement agencies involved in order to minimize the impact of whatever they find.