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.”

The ballooning size —and cost—of the president’s legal team is eloquent testimony to how seriously the administration is taking Mueller’s probe.

Robert Mueller. Alex Wong/Getty Images 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.

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.

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.

A colorized image of President Richard Nixon. Getty Images/Algorithmia 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.