It’s been clear at least since the appointment of Special Counsel Robert Mueller that President Donald Trump feels himself to be in potential legal jeopardy. The ballooning size—and cost—of the president’s legal team is eloquent testimony to how seriously the administration is taking Mueller’s probe. But for all the questions about what, if any, crimes may have been committed by Trump or members of his campaign team, most people remain unclear what might happen if the day arrives when Mueller looks around at his staff and says, “Yep, we’ve got a criminal case.”

What follows is an informed citizen’s guide to the obstacles that stand between Mueller deciding that a crime was committed and either impeachment of President Trump or prosecution of any Trump-linked suspects. The hurdles for Mueller are many, the obstructive powers of the presidency are great, and the ultimate verdict on Mueller’s work will likely rest with congressional Republicans who have so far shown little appetite for confronting the unsavory side of their party’s leader.

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1. Robert Mueller’s authority: “special counsel,” not “independent counsel.”

Robert Mueller was appointed “special counsel” to head the investigation into Russian meddling in the 2016 election. Mueller, however, does not hold the same office or wield the same powers as Independent Counsel Kenneth Starr, President Clinton’s nemesis in the Lewinsky affair.

The office of “independent counsel” was created by the post-Watergate Ethics in Government Act of 1978. An independent counsel was selected by a special panel of federal judges. He wielded all of the investigative and prosecutorial authority of the Department of Justice and was specifically charged with making recommendations to Congress about possible impeachable offenses. He could only be removed by Congress through impeachment or “by the personal action of the Attorney General and only for good cause, physical or mental disability.” “Good cause” did not include the attorney general’s disagreement with the counsel’s professional judgments. And, if removed by the attorney general, the independent counsel could appeal to the U.S. Court of Appeals for the District of Columbia Circuit.

But the independent counsel statute lapsed in 1999, and the office of special counsel is a different, far less independent, animal. A special counsel is appointed by the attorney general, or in this case the deputy attorney general. He is difficult to remove—“good cause” is required—but removal authority rests with the attorney general, and there is no appeal. More importantly, a special counsel wields not the full powers of the Department of Justice but only the powers of a U.S. attorney. Thus, while the special counsel can authorize criminal indictments, his authority is subordinate to the attorney general—or in this case, the deputy attorney general—who is empowered to overrule him on any “investigative or prosecutorial step.” Moreover, a special counsel has no express authority to draw any conclusions or make any recommendations about impeachment.

If Mueller were to conclude that the president committed an impeachable offense, he could, in theory, present that conclusion in his final report to his DOJ superiors. There are powerful reasons to doubt that he would. Mueller is a careful, meticulous lawyer who has surrounded himself with other lawyers of the same stripe. He and his staff will be quite conscious of the fact that the DOJ regulations governing his office differ from the lapsed independent counsel statute in omitting any power or responsibility to draw conclusions or make recommendations about impeachment. They might, as Special Counsel Leon Jaworski famously and controversially did during Watergate, recommend naming the president as an unindicted co-conspirator in a criminal case against someone else. But that is likely as far as they would—or should—go. It’s worth noting that, as in the case of Nixon, doing so would send a clear signal to Congress about impeachment.

2. Jeff Sessions’ recusal does not give Mueller free rein.

Mueller was selected by Deputy Attorney General Rod Rosenstein because Attorney General Jeff Sessions recused himself from decisions in the Russia investigation. Some have assumed that this effectively gives Mueller full authority to use his own judgment. It doesn’t. First, Sessions’ recusal has already proven remarkably elastic. Despite it, he was actively involved in the decision to fire FBI Director James Comey, a decision Trump admitted was directly related to the Russian investigation.

Second, even if Sessions stays away, Mueller remains subordinate to Rosenstein. The deputy attorney general seems like a straight shooter and has promised that Mueller will have “full independence … to conduct the investigation.” Nonetheless, under DOJ regulations, Rosenstein, not Mueller, gets the final call on what to do with the results of that investigation. That matters. A fair assessment of Rosenstein is that is that he will be neither a toady for Trump nor a rubber stamp for Mueller. But there is likely to be plenty of room for honest disagreement in this affair, and Rosenstein may well give some benefit of the doubt to the president he serves.

Third, Rosenstein wrote the letter providing justification for Comey’s firing and has admitted that Comey’s dismissal may come within Mueller’s writ. Thus, he may have to recuse himself, ceding authority over Mueller to Associate Attorney General Rachel Brand, a capable person, but a Republican political functionary rather than a career prosecutor. So, in the end, it may be Brand, not Mueller, who decides whether criminal charges are filed against anyone.

3. The president himself is effectively immune from criminal indictment.

Regardless of whether President Trump has committed a crime, he surely will not be indicted while in office. There is serious debate about whether a sitting president can constitutionally be indicted. Many scholars say no. Others say yes. But what the eggheads think is beside the point, because the official Justice Department position has long been no. It is implausible in the highest degree that either Rosenstein or Brand would reverse that position to authorize indictment of their boss.

There is no path to criminal charges against Trump himself outside of DOJ. The Fifth Amendment requires that federal felonies be commenced by grand jury indictment, and Rule 7 of the Federal Rules of Criminal Procedure provides that no indictment, even one approved by a grand jury, is valid unless signed by “an attorney for the government.” Thus, no federal felony prosecution of Trump, or anyone else, can occur without Department of Justice consent.

Moreover, if indicted, the president could probably pardon himself (though his pardon power doesn’t extend to impeachment).

4. Mueller’s decisions about criminal charges still matter on the impeachment question.

Even though Mueller can’t indict the president and isn’t authorized to make an official recommendation about impeachable conduct, his decisions could endanger the president. If Trump has committed impeachable offenses, he will not have done so alone, but in concert with his family, aides, or political supporters. Building an impeachment case against Trump is just like building a criminal case against a corporate executive or organized crime boss. You start with subordinates and work your way up.

If Trump’s subordinates have committed crimes in which their boss is implicated, the public exposure of the evidence against them that would flow from an indictment would allow Congress and the public to draw conclusions about impeachment Mueller probably won’t. And if the prediction above that Mueller won’t exceed his official brief proves wrong and Mueller does offer an opinion on impeachable offenses, the danger to Trump would be immeasurably higher.

5. DOJ cannot hide a Mueller recommendation of indictment.

Suppose Mueller decides that a Trump associate should be indicted but is overruled by his Justice Department superior. Would the matter then die in silence? No. DOJ special prosecutor regulations require that the attorney general—or here his designate—report disagreements of this kind to Congress. That’s a big deal. Congressional Republicans wouldn’t be able to bury a veto of Mueller’s decision in the bowels of DOJ by not requesting disclosure or refusing to authorize a subpoena for the information.

6. If Mueller decides against criminal charges, things get tricky.

Mueller’s work endangers Trump even if no indictment results. The official scope of Mueller’s investigation seems narrow. The only subject mentioned in Rosenstein’s appointment letter is collusion between the Russian government and the Trump campaign. But the letter also authorizes inquiry into matters “arising from” the investigation and any efforts to obstruct justice. Mueller is famously painstaking. His investigation of Trump-Russia connections will involve not only low-hanging fruit like Donald Trump Jr.’s meeting with Russian figures promising electoral help to his father but meticulous review of the communications and finances of everyone connected with Trump’s campaign. It is entirely plausible that Mueller will unearth crimes or dodgy behavior by Trump and associates not directly linked to Russia. The big question is how much of what Mueller uncovers will become public.

On any matter where Mueller decides not to indict, either because he thinks there is insufficient evidence or he lacks jurisdiction, the path to disclosure is rocky. Unlike the old post-Watergate independent counsel, a special counsel like Mueller is just another DOJ official who has no independent authority to make general reports to Congress.

The longstanding DOJ norm is not to go public with the details of closed investigations. Jim Comey was widely—and properly—condemned for violating that norm by volunteering information about the decision not to prosecute Hillary Clinton for her use of a private email server during her time at the State Department. Rosenstein relied on that violation in recommending Comey’s dismissal. This Justice Department will not easily disclose information not directly connected to an actual indictment.

This does not mean that Congress would be barred from seeing whatever Mueller finds. But it would have to press hard to get it by invoking some combination of its oversight, investigative, and impeachment authority. So long as Republicans control both houses, it is fair to wonder how hard they would press. In any case, if the White House directed DOJ to resist disclosure—and it surely would—the resulting fight would be long and rancorous. A sufficiently determined Congress would probably prevail, but even that is uncertain.

7. Trump could stop or frustrate the Mueller probe.

Given the grave risks Mueller presents to the Trump presidency, could Trump stop the investigation right now? Yes.

First, the president has the undoubted power to order Mueller’s DOJ superior—whether Rosenstein or Brand—to fire him and shut down the investigation. If that person refused, the president could fire that person, give the same order to the next in line of DOJ seniority, and keep firing people until he found someone willing to follow orders. It would essentially be a replay of Nixon’s Saturday Night Massacre firing of Archibald Cox.

Alternatively, the president could protect subordinates targeted by Mueller and frustrate efforts to turn them against him by issuing preemptive pardons. Article II, Section 2, of the Constitution gives him unquestioned power to pardon any “offense against the United States, except in cases of impeachment.” And there is precedent for preemptive pardons in President Gerald Ford’s pardon of Richard Nixon.

Either a massacre or a pardon would carry obvious political costs, but whether those costs would be high enough to deter a man of Trump’s temperament is an open question. More importantly, if a president misuses his legitimate powers for illegitimate ends, that misuse can itself be an impeachable offense. Either a Saturday Night Massacre replay or pardons employed to protect Trump or his associates from legal jeopardy might constitute impeachable conduct.

This last, most desperate, Trumpian move would test the mettle of Republicans, and our collective dedication to the rule of law itself, more than any other. I wish I were more confident we would pass the test.