Special counsel Robert Mueller said indicting President Donald Trump was “not an option” this week, citing a longstanding Justice Department policy that shields a sitting president from criminal indictments and prosecution.

Now Sen. Elizabeth Warren (D-MA) says she would change the policy as president.

Warren, among the first major Democratic 2020 candidates to call for Trump’s impeachment, released a two-part proposal on presidential powers Friday. First, she called on Congress to pass a law clarifying that the president of the United States is subject to the same federal criminal code as everyone else. Second, she pledged to appoint an attorney general and assistant AG who would change current Justice Department policy around indicting sitting presidents.

“Donald Trump believes that he can violate the law, and he believes that the role of the Department of Justice is to help him get away with it. That’s not how our country is supposed to work,” Warren wrote. “I pledge to nominate an [Office of Legal Counsel] head who will reverse the Watergate-era rule that a President cannot be indicted for criminal behavior.”

On Wednesday, Mueller reiterated he was operating under DOJ policy, as presented by the Office of Legal Counsel, that a sitting president cannot be charged with a federal crime.

“Under longstanding department policy a president cannot be charged with a federal crime while he is in office,” Mueller said. “That is unconstitutional. ... The special counsel’s office is part of the Department of Justice and by regulation it was bound by that department policy. Charging the president with a crime was, therefore, not an option we could consider.”

To be clear, what Mueller is referring to is not something expressly written in the Constitution. It’s a large gray area in the nation’s body of law — which Warren says she would address as president.

The question of presidential immunity, briefly explained

The closest the Supreme Court has come to answering the question of presidential immunity recently is a 1997 ruling in Clinton v. Jones, which maintained that a president is subject to civil lawsuits. But whether a sitting president can be subject to criminal prosecution remains an unanswered question in the courts.

Upon review in 1973 and again in 2000, OLC concluded that the best way to address criminal charges is to wait until a president leaves office, leaving impeachment as the avenue for accountability.

As Vox’s Dylan Matthews explained, the most famous argument in favor of making presidents immune from criminal prosecution is from a 1997 law review article by Yale constitutional law professor Akhil Amar and a then-student of his, Brian Kalt, who’s now a law professor at Michigan State University:

Amar and Kalt argue that the president is a unique official, as the sole person ultimately in charge of the executive branch. “If he is arrested, so too is the executive branch of the government,” they write. This distinguishes him from a normal legislator or judge, who can be prosecuted, because there are plenty of other judges and legislators who can carry on their work. “Any distraction of the President from his duties is much more significant than similar distractions of these other, prosecutable officials, and has a much bigger impact on the well-being of the nation and all its People,” they conclude.

But even Kalt says this is unsettled territory. There is an argument to be made that the president should be subject to the same legal standard as everybody else, and that there are structures in place to address a president with “distractions” from his executive duties.

The investigation into Trump, and the special counsel report outlining evidence that Trump may have obstructed justice, has raised this issue into the forefront once again.

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