Paul Callan is a CNN legal analyst, a former New York homicide prosecutor, and current counsel at the New York law firm of Edelman & Edelman PC, focusing on wrongful conviction and civil rights cases. Follow him on Twitter @paulcallan. The opinions expressed in this commentary are his own.

(CNN) Can the president of United States be prosecuted for obstruction of justice under the US Constitution? The answer is yes, he most certainly can -- though the initial punishment for such an offense is impeachment and removal from office. The Constitution enables impeachment for "high crimes and misdemeanors," but does not define what those offenses are, though they could in theory include obstruction.

The more complicated question is the one that comes next. Can a sitting president face criminal prosecution for obstruction of justice? According to experts who spoke to the ABA Journal , the prevailing view among legal scholars seems to be that a president can be prosecuted only after he no longer holds the title of "President of the United States."

On Monday, President Trump, as a part of his usual frenetic pattern of Twitter activity, urged Americans to watch his favored news network, Fox, where Harvard professor of law emeritus Alan Dershowitz was trotting out his illogical theory that the president cannot be indicted for "obstruction of justice" because, under Article II of the Constitution, the president is responsible for all federal law enforcement investigative activity. Mr. Dershowitz ominously warned that prosecuting the president for such an offense would lead to a "constitutional crisis." Mr. Trump's tweet used Dershowitz's appearance to repeat his favorite refrain, that Robert Mueller's investigation into ties between his campaign and Russia is a "witch hunt."

The President may have wide constitutional powers, but he is not above the law. If he were to use the constitutional powers suggested by Professor Dershowitz as a matter of presidential discretion under Article II, he would distort the system of checks and balances so carefully designed by the Founding Fathers to keep the power of the nation's chief executive constrained by legislative and judicial branches of government.

The Dershowitz argument, in a nutshell, is that since the Constitution has put the president in charge of federal law enforcement in the United States, he cannot be prosecuted for exercising his discretion to direct how law enforcement authorities use their limited resources. Proponents of the Dershowitz view -- Mr. Trump deems his segment a "must watch" -- might cite the Obama administration's reallocation of Justice Department resources as an example of the perfect legality of a presidential decision to shift federal law enforcement investigative priorities from one kind of crime to another.

Read More