There is not much guidance on this. There is the Constitution, a couple of cases and Department of Justice guidelines.
The Constitution, may the Framers burn in Hell, provides that,
"The President, Vice President and all civil Officers of the United States, shall be removed from Office on Impeachment for, and Conviction of, Treason, Bribery, or other high Crimes and Misdemeanors."
-Article Two Section 4.
Being a constitutional literalist for the moment I do not see Article Two, Section 4 barring a criminal prosecution of a sitting president. What if he was convicted in the criminal courts and then impeached by the House and convicted in the Senate? But, now a textualist, the context is all criminal. It is reasonable to interpret Article Two Section 4 as granting a sitting president immunity from criminal prosecution in the courts with the only remedy impeachment and it is my understanding that Article Two Section 4 has been interpreted as granting immunity from criminal prosecution.
Neither does Article Two Section 4 prescribe the criminal conduct temporally. What if it occurred before the president was sworn in? What if he murdered somebody twenty years before and walked? Could he still be impeached? Criminally prosecuted? What if, as in Trump's case, crimes were committed before he was sworn in but not discovered until afterwards? What if crimes were committed both before and after taking office? My understanding is that the temporal does not matter, a president cannot be prosecuted criminally while he sits nor after he leaves office. But I do not think this has been dealt with at all. Do we have any guidance on hypothetical situations like the following? After a president leaves office it is discovered that he murdered someone before, during, or after his presidency? It is hard for me to believe that Article Two Section 4 gives a president immunity for life for all crimes committed during his life. Let's break that down: before his presidency but not discovered until he became president? My understanding is the president could not be criminally prosecuted for the before-presidency murder during his presidency. Could he be prosecuted for a before murder after he left office? My understanding...yes but. But show me a case. You can't. There is no law I am aware of on the question. What if Trump murdered Melania right now, while president? Could not be criminally prosecuted even for murder while president. Article Two Section 4 covers the entire sweep of criminal law from treason down to misdemeanors and provides only for impeachment as the remedy. What if he murdered Melania now but his involvement was not uncovered until after his presidency. I think so but I don't know. Does it matter that the crime was within or without his scope of duties as president? I don't think it matters. If the crime was committed during his presidency, murder (unrelated to scope) or treason (related), my understanding is he cannot be prosecuted criminally while he sits.
What does "criminal prosecution" mean? Indicted? Standing trial? Sentenced to prison? In this context of crimes committed at any time by a sitting president criminal prosecution certainly means the latter two, standing trial and sentenced. In state and federal criminal prosecutions of non sitting presidents a criminal prosecution is deemed to have commenced upon indictment. Article Two Section 4 does not explicitly bar indictment and there is some reason to believe that the Framers did not intend to bar indictment, what they wanted to prevent was a sitting chief executive being taken away from his duties by having to attend his own criminal trial. Department of Justice guidelines since 2000 provide that a sitting president "should not" be indicted. But Walter Dellinger, head of DOJ's Office of Legal Counsel from 1993-96, thinks a sitting president "could be" indicted, just not tried in court. Walter suggests Robert Mueller ask the office to reconsider. Eh, I don't think Mueller will do that. I don't think a sitting president can be indicted.
State and federal? Yes, state and federal both. For reasons of federalism and from the Constitution itself both state and federal criminal prosecution of a sitting president are barred.
The Constitution does not speak to civil law prosecution, where only money is at stake, only to criminal. Clinton v Jones, 520 U.S. 681 (1997),in which Walter Dellinger represented Clinton, held unanimously for Jones that a civil suit against a sitting president was permitted, inconvenience to the incumbent be damned.
In the sort-of considered opinion of the undersigned, therefore, what the law can do when it gets to Trump, and by God it's almost there, is sue him in civil court for, e.g., racketeering, conspiracy, anything. Just not criminally, not for obstruction of justice, perjury, nothin'. For crimes, see Article Two Section 4.
The Constitution, may the Framers burn in Hell, provides that,
"The President, Vice President and all civil Officers of the United States, shall be removed from Office on Impeachment for, and Conviction of, Treason, Bribery, or other high Crimes and Misdemeanors."
-Article Two Section 4.
Being a constitutional literalist for the moment I do not see Article Two, Section 4 barring a criminal prosecution of a sitting president. What if he was convicted in the criminal courts and then impeached by the House and convicted in the Senate? But, now a textualist, the context is all criminal. It is reasonable to interpret Article Two Section 4 as granting a sitting president immunity from criminal prosecution in the courts with the only remedy impeachment and it is my understanding that Article Two Section 4 has been interpreted as granting immunity from criminal prosecution.
Neither does Article Two Section 4 prescribe the criminal conduct temporally. What if it occurred before the president was sworn in? What if he murdered somebody twenty years before and walked? Could he still be impeached? Criminally prosecuted? What if, as in Trump's case, crimes were committed before he was sworn in but not discovered until afterwards? What if crimes were committed both before and after taking office? My understanding is that the temporal does not matter, a president cannot be prosecuted criminally while he sits nor after he leaves office. But I do not think this has been dealt with at all. Do we have any guidance on hypothetical situations like the following? After a president leaves office it is discovered that he murdered someone before, during, or after his presidency? It is hard for me to believe that Article Two Section 4 gives a president immunity for life for all crimes committed during his life. Let's break that down: before his presidency but not discovered until he became president? My understanding is the president could not be criminally prosecuted for the before-presidency murder during his presidency. Could he be prosecuted for a before murder after he left office? My understanding...yes but. But show me a case. You can't. There is no law I am aware of on the question. What if Trump murdered Melania right now, while president? Could not be criminally prosecuted even for murder while president. Article Two Section 4 covers the entire sweep of criminal law from treason down to misdemeanors and provides only for impeachment as the remedy. What if he murdered Melania now but his involvement was not uncovered until after his presidency. I think so but I don't know. Does it matter that the crime was within or without his scope of duties as president? I don't think it matters. If the crime was committed during his presidency, murder (unrelated to scope) or treason (related), my understanding is he cannot be prosecuted criminally while he sits.
What does "criminal prosecution" mean? Indicted? Standing trial? Sentenced to prison? In this context of crimes committed at any time by a sitting president criminal prosecution certainly means the latter two, standing trial and sentenced. In state and federal criminal prosecutions of non sitting presidents a criminal prosecution is deemed to have commenced upon indictment. Article Two Section 4 does not explicitly bar indictment and there is some reason to believe that the Framers did not intend to bar indictment, what they wanted to prevent was a sitting chief executive being taken away from his duties by having to attend his own criminal trial. Department of Justice guidelines since 2000 provide that a sitting president "should not" be indicted. But Walter Dellinger, head of DOJ's Office of Legal Counsel from 1993-96, thinks a sitting president "could be" indicted, just not tried in court. Walter suggests Robert Mueller ask the office to reconsider. Eh, I don't think Mueller will do that. I don't think a sitting president can be indicted.
State and federal? Yes, state and federal both. For reasons of federalism and from the Constitution itself both state and federal criminal prosecution of a sitting president are barred.
The Constitution does not speak to civil law prosecution, where only money is at stake, only to criminal. Clinton v Jones, 520 U.S. 681 (1997),in which Walter Dellinger represented Clinton, held unanimously for Jones that a civil suit against a sitting president was permitted, inconvenience to the incumbent be damned.
In the sort-of considered opinion of the undersigned, therefore, what the law can do when it gets to Trump, and by God it's almost there, is sue him in civil court for, e.g., racketeering, conspiracy, anything. Just not criminally, not for obstruction of justice, perjury, nothin'. For crimes, see Article Two Section 4.