So why hasn't Trump been charged yet?
Here's a very good explanation from August 2017 of this complex issue. In short, you need to impeach and remove him from office first, then try him on criminal charges.
Commentary: Can a sitting U.S. president be prosecuted?
Cass R. Sunstein
Bloomberg View
Can a sitting president be prosecuted? Might Donald Trump, or any president, face the prospect of jail?
A memorandum of law, written in 1998 but released last week, concludes that the answer is a qualified "yes." The memorandum was written by Chapman University law professor Ronald Rotunda, who was then at the University of Illinois, for Kenneth Starr, the independent counsel appointed to investigate President Bill Clinton.
Rotunda's memorandum is learned, illuminating and impressively detailed. The issue is both tough and unsettled. But there's a better answer: an unqualified "no."
The drafters of the Constitution spent a lot of time on the question of how to respond to presidential wrongdoing. Their remedy was impeachment (by the House of Representatives) and then conviction (by the Senate), which could occur for "Treason, Bribery, or other high Crimes and Misdemeanors."
But what happens if the president is convicted by the Senate? Here's the constitutional answer:
"Judgment in Cases of Impeachment shall not extend further than to removal from office, and disqualification to hold and enjoy any Office of honor, Trust or Profit under the United States: but the Party convicted shall nevertheless be liable and subject to Indictment, Trial, Judgment and Punishment, according to Law."
A reasonable interpretation of this provision is that it sets out a temporal sequence: Impeachment, then conviction and removal from office — and only after that, indictment, trial, judgment and punishment.
Alexander Hamilton seemed to read the provision exactly that way: "The President of the United States would be liable to be impeached, tried, and, upon conviction of treason, bribery, or other high crimes or misdemeanors, removed from office; and would afterwards be liable to prosecution and punishment in the ordinary course of law."
That means you can't indict and try a sitting president. He has to be removed first.
True, this interpretation isn't inevitable. You could read the text to mean only that the consequence of conviction is removal from office, and that a convicted president can be prosecuted — but to be silent on, and so not to resolve, the question whether a president can be prosecuted for crimes while in office. On that interpretation, nothing in the Constitution rules out a prosecution of the president for (say) obstruction of justice or for perjury.
Rotunda also emphasizes that a president might commit crimes, such as battery, shoplifting and document destruction, that may not be "high" in the constitutional sense, and so not a legitimate basis for impeachment. If he's immune from prosecution, does the president get a free ride? Since the founders believed no one should be above the law, Rotunda doesn't think that makes a lot of sense.
Importantly, though, he does not contend that the president can be prosecuted for actions he undertakes in his official capacity. His conclusion that a sitting president can be prosecuted is strictly limited to actions committed before becoming president, and actions that a president does not undertake in his role as president, such as Clinton's alleged perjury. (True, the line between the official and unofficial acts can be thin.)
The problem with Rotunda's argument is that presidential immunity from criminal prosecution — while in office — is a pretty reasonable inference from the constitutional design. Whether or not you like the current occupant of the Oval Office, he has an awesome array of responsibilities. Even on a slow day, numerous decisions reach his desk. They might involve potential terrorist attacks, a looming epidemic, immigration or air pollution. Facing a criminal prosecution seems fatally incompatible with the president's constitutional role.
Aware of this argument, Rotunda notes that the Supreme Court allowed Paula Jones' sexual harassment suit to go forward against Bill Clinton, notwithstanding Clinton's argument that to do his job, a sitting president needs to have immunity against such lawsuits. Among other things, the Supreme Court answered that trial judges could find ways to accommodate the president's schedule. Why isn't the same thing true for a criminal prosecution?
That's a fair question, but a criminal proceeding is unique, and the problem isn't really about scheduling. Realistically speaking, any White House would be pretty well disabled if the president is under a criminal indictment and faces the prospect of trial and imprisonment.
Rotunda is aware of the risk, and leaves open the possibility that imprisonment itself might be delayed, so that the prosecution would not compete with the impeachment mechanism. But that's hardly sufficient. The question is whether the president's ability to perform his constitutional functions would be impaired by the prosecution itself. There's little doubt that it would.
Does this mean that the president is above the law? Not at all. In cases of serious wrongdoing, and breaches of public trust, the Constitution provides a remedy: impeachment.
